Origin of Isoforms and Interaction with Nucleic Acids
Phosphoprotein B23 (Mr /pI = 38,000/5.1) is a RNA-associated protein located predominantly in the granular component of the nucleolus (Spector et al., 1984) proposed to be an assembly factor in the later stages of ribosome biogenesis. More recently, Borer et al. (1989) suggested that the protein is also a carrier of ribosomal proteins into the nucleus. Electrophoretic and immunoblot analyses in this and other laboratories (Chan et al., 1985) indicate the presence of at least two forms of the protein, differing slightly in molecular mass. Recently, a full-length cDNA for rat protein B23 was isolated and sequenced (Chang et al., 1988). During the course of screening a cDNA library a second cDNA clone was observed. The two cDNAs contained identical 5′ regions but distinct 3′ regions. This led to our first question: do the two isoforms arise from separate genes or from different expressed segments within a single gene?
KeywordsSucrose Magnesium Carboxyl Fractionation Polypeptide
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