Crystallographic Studies of Two Proteins that Bind Single-Stranded DNA

Abstract

Although most protein-DNA recognition phenomena governing the expression of genetic information are exercised at the level of double- stranded DNA, a vast number of salient cellular events utilizing nucleic acids involve primarily or exclusively ssDNA or RNA. Indeed, one of the first events to occur following recognition and binding of activating proteins to native DNA is the unwinding of the duplex to expose the single strands. Events that include the replication of DNA to produce daughter strands, the transcription of DNA to RNA, viral replication and infection, the repair of DNA, genetic recombination, and DNA modification and degradation all involve primarily single-stranded forms of DNA. Viruses frequently possess single-stranded nucleic acid genomes, and virtually all RNA structures such as tRNA, ribosomal RNAs, and messenger RNAs are single stranded. It is further likely that other forms of nucleic acid that we now know little about, such as the viroids, will involve exclusively single-stranded forms. All of these single-stranded nucleic acids, both RNA and DNA, exhibit a host of both intra- and intermolecular interactions in arriving at their active or native state.