Springer Nature is making SARS-CoV-2 and COVID-19 research free. View research | View latest news | Sign up for updates

Morphology of transcription units inDrosophila melanogaster


We have used an electron microscopic analysis to define and to characterize active transcription units ofDrosophila melanogaster. The lengths and spacings of nascent ribonuclear protein (RNP) fibers were determined on embryonic chromatin that was spread using techniques introduced by Miller and Beatty (1969). The data are consistent with the occurrence of specific sites of transcription initiation and termination. We apply the termtranscription unit (TU) to a chromatin region bounded by these control sites. Two classes of TUs are active inDrosophila melanogaster embryonic cells—those synthesizing ribosomal RNA and those synthesizing non-ribosomal RNA. The classes can usually be distinguished on the basis of TU size, chromatin morphology and inferred DNA packing ratio, frequency of RNP fibers (number of fibers per μm of chromatin), and the solitary vs. tandem repeat occurrence of fiber arrays. The results indicate that nonribosomal transcription units have lengths in accord with the expectation that DNA of each chromomere is transcribed as a unit.—Some nascent fiber arrays inD. melanogaster have more complex patterns of RNP fiber lengths. We suggest that these are a consequence of cleavage of RNP fibers at specific sites during transcription. — These sites of transcriptional control and the amounts of DNA between them provide a basis for further relating units of transcription to units of gene function.

This is a preview of subscription content, log in to check access.


  1. Angelier, N., Lacroix, J.C.: Complexes de transcription d'origines nucleolaire et chromosomique d'ovocytes de Pleurodeles waltlii et P. poireti (Amphibiens, Urodeles). Chromosoma (Berl.)51, 323–335 (1975)

  2. Axel, R., Cedar, H., Felsenfeld, G.: The structure of the globin genes in chromatin. Biochemistry (Wash.)14, 2489–2495 (1975)

  3. Beermann, W.: Chromomeres and genes. In: Results and problems-cell differentiation, Vol. 4 W. Beermann, J. Reinert and H. Ursprung, eds. Berlin-Heidelberg-New York: Springer 1972

  4. Bishop, J.O., Morton, J.G., Rosbash, M., Richardson, M.: Three abundance classes in HeLa cell messenger RNA. Nature (Lond.)250, 199–204 (1974)

  5. Bordier, C., Dubochet, J.: Electron microscopic localization of the binding sites of Escherichia coli RNA polymerase in the early promoter region of T7 DNA. Europ. J. Biochem.44, 617–624 (1974)

  6. Chooi, W.Y., Laird, C.D.: DNA and polyribosome-like material in lysates of mitochondria of Drosophila melanogaster. J. molec. Biol.100, 475–508 (1976)

  7. Daneholt, B.: Giant RNA in a Balbiani ring. Nature (Lond.) New Biol.240, 229 (1972)

  8. Darlix, J.-C., Dausse, J.-P.: Localization of Escherichia coli RNA polymerase initation sites in T7 DNA early promoter region. F.E.B.S. Letters50, 214–218 (1975)

  9. Darnell, J.E., Jelinek, W.R., Molloy, G.R.: Biogenesis of m-RNA: Genetic regulation in mammalian cells. Science181, 1212–1221 (1973)

  10. Davis, R.W., Hyman, R.W.: Physical locations of the in vitro RNA initiation site and termination sites of T7 M DNA. Cold Spr. Harb. Symp. quant. Biol.39, 269–281 (1970)

  11. Derksen, J., Trendelenburg, M.F., Scheer V., Franke, W.: Spread chromosomal nucleoli of Chironomus salivary gland. Exp. Cell Res.80, 476–479 (1973)

  12. Dunn, J.J., Studier, F.W.: Processing, transcription, and translation of bacteriophage T7 messenger RNAs. Brookhaven Symp. Biol.26, 267–276 (1975)

  13. Flanagan, J.R.: Maximum likelihood procedures for evaluating data of chromatin-associated fiber arrays.(Appendix to Laird et al., 1976). Chromosoma (Berl.)58, 191–192 (1976)

  14. Foe, V.E.: Activation of transcription units during the embryogenesis of Oncopeltus fasciatus. Ph. D. dissertation, University of Texas, Austin (1975)

  15. Foe, V.E., Wilkinson, L.E., Laird, C.D.: Comparative organization of active transcription units in Oncopeltus fasciatus. Cell9, 131–146 (1976)

  16. Glätzer, K.H.: Visualization of gene transcription in spermatocytes of Drosophila hydei. Chromosoma (Berl.)53, 371–380 (1975)

  17. Gottesfeld, J.M., Murphy, R.F., Bonner, J.: Structure of transcriptionally active chromatin. Proc. nat. Acad. Sci. (Wash.)72, 4404–4408 (1975)

  18. Hamkalo, B.A., Miller, O.L., Jr.: Electron microscopy of genetic activity. Ann. Rev. Biochem.42, 379–396 (1973)

  19. Hamkalo, B.A., Miller, O.L., Jr., Bakken, A.H. Ultrastructure of eukaryotic genomes. Cold Spr. Harb. Symp. quant. Biol.38, 915 (1973)

  20. Hennig, W., Meyer, G.F., Hennig, I., Leoncini, O.: Structure and function of the Y chromosome of Drosophila hydei. Cold Spr. Harb. Symp. quant. Biol.38, 673–683 (1973)

  21. Hochman, B.: Analysis of a whole chromosome in Drosophila. Cold Spr. Harb. Symp. quant. Biol.38, 581–589 (1974)

  22. Judd, B.H., Shen, M.W., Kaufman, T.C.: The anatomy and function of a segment of the X chromosome of Drosophila melanogaster. Genetics71, 139–156 (1972)

  23. Kierszenbaum, I.L., Trez, L.L.: Transcription sites in spread meiotic prophase chromosomes from mouse spermatocytes. J. Cell Biol.63, 923–935 (1974)

  24. Lacy, E., Axel, R.: Analysis of DNA of isolated chromatin subunits. Proc. nat. Acad. Sci. (Wash.)72, 3978–3982 (1975)

  25. Laird, C.D.: DNA of Drosophila chromosomes. Ann. Rev. Genet.7, 177–204 (1974)

  26. Laird, C.D., Wilkinson, L.E., Foe, V.E., Chooi, W.Y.: Analysis of chromatin-associated fiber arrays. Chromosoma (Berl.)58, 169–190 (1976)

  27. Lamb, M.M., Laird, C.D.: Size of poly A-containing RNAs in Drosophila melanogaster embryos. Biochem. Genet.14, 357–371 (1976a)

  28. Lamb, M.M., Laird, C.D.: Increase in nuclear poly A-containing RNA at syncytial blastoderm in Drosophila melanogaster embryos. Develop. Biol.52, 31–42 (1976b)

  29. Lengyel, J., Penman, S.: hnRNA size and processing as related to DNA content in two dipterans: Drosophila and Aedes. Cell5, 281–290 (1975)

  30. Lindsley, D.L., Grell, E.H.: Genetic variations of Drosophila melanogaster. Carnegie Inst. Wash. Publ.627 (1968)

  31. McKnight, S.L., Miller, O.L., Jr.: Ultrastructural patterns of RNA synthesis during early embryogenesis of D. melanogaster. Cell8, 305–319 (1976)

  32. Meyer, G.F., Hennig, W.: The nucleolus in primary spermatocytes of Drosophila hydei. Chromosoma (Berl.)46, 121 (1974)

  33. Miller, O.L., Jr., Bakken, A.H.: Morphological studies of transcription. Acta endocr. (Kbh.), Suppl.168, 155–157 (1972)

  34. Miller, O.L., Jr., Beatty, B.R.: Visualization of nucleolar genes. Science164, 955 (1969)

  35. Miller, O.L., Jr., Beatty, B.R., Hamkalo, B.A., Thomas, C.A., Jr.: Electron microscopic visualization of transcription. Cold Spr. Harb. Symp. quant. Biol.35, 505 (1970)

  36. Perry, R.P., Cheng, T.Y., Freed, J.J., Greenberg, J.R., Kelley, D.E., Tartof, K.D.: Evolution of the transcriptional unit of ribosomal RNA. Proc. nat. Acad. Sci. (Wash.)65, 609 (1970)

  37. Robertson, H., Dickson, E.: RNA processing and the control of gene expression. Brookhaven Symp. Biol.26, 240–266 (1975)

  38. Scheer, U., Trendelenburg, M.F., Franke, W.W.: Transcription of ribosomal RNA cistrons. Correlation of morphological and biochemical data. Cell. Res.80, 175–190 (1973)

  39. Sommerville, J., Malcolm, D.B.: Transcription of genetic information in amphibian oocytes. Chromosoma (Berl.)55, 183–208 (1976)

  40. Spring, H., Trendelenburg, M.F., Scheer, U., Franke, W.F., Herth, W.: Structural and biochemical studies of the primary nucleus of two green algal species, Acetabularia mediterranea and Acetabularia major. Cytobiologie10, 1–65 (1974)

  41. Trendelenburg, M.F.: Morphology of ribosomal RNA cistrons in oocytes of the water beetle Dytiscus marginalis. Chromosoma (Berl.)48, 119 (1974)

  42. Trendelenburg, M.F., Scheer, V., Franke, W.W.: Structural organization of ribosomal DNA in oocytes of the house cricket. Nature (Lond.) New Biol.245, 167–170 (1973)

  43. Trendelenburg, M.F., Spring, H., Scheer, V., Franke, W.W.: Morphology of nucleolar cistrons in a plant cell, Acetabularia mediterranea. Proc. nat. Acad. Sci. (Wash.)71, 3626 (1974)

  44. Turner, S.H., Laird, C.D.: Diversity of RNA sequences in Drosophila melanogaster. Biochem. Genet.10, 263–274 (1973)

  45. Weinstein, A.: Heredity and development. In: Chemistry in medicine (J. Stieglitz, ed.). New York: The Chemical Foundation, 1928

  46. Weintraub, H., Groundine, M.: Transcriptionally active and inactive conformations of chromosomal subunits. Science (in press, 1976)

  47. Zalokar, M.: Autoradiographic study of protein and RNA formation during early development of Drosophila eggs. Develop. Biol.49, 425–437 (1976)

Download references

Author information

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Laird, C.D., Chooi, W.Y. Morphology of transcription units inDrosophila melanogaster . Chromosoma 58, 193–218 (1976).

Download citation


  • Tandem Repeat
  • Specific Site
  • Fiber Length
  • Control Site
  • Active Transcription