Preliminary evidence indicates that the Drosophila Structure Binding Protein 1 (sbp1) gene is an excellent candidate for involvement in DNA recombination, replication, and/or repair. The spb1 gene is a single copy gene producing three different transcripts that are enriched in tissues and life stages involved in rapid cell division. The SPB1:beta-galatosidase fusion protein preferentially binds three-stranded DNA structures in a sequence independent manner, and appears to possess a strand displacement activity. The protein predicted from the nucleic acid sequence of sbp1 cDNAs shares some sequences similarity with prokaryotic DNA ligases. The primary objective of this proposal is to define, at single- nucleotide resolution, the specific binding determinant present in three-stranded DNA structures that is preferentially recognized and bound by SBP1. This will be accomplished by first chemically probing isolated structures to model the three dimensional structure of the DNA. Regions that are accessible to the probe are predicted to be either single stranded or distorted double stranded regions in DNA. Subsequently, the relative binding affinity of SBP1 for modified versions of the preferred binding substrate will be assayed. Modifications resulting in a reduction or elimination of binding will indicate the importance of a determinant for SPB1 binding. %%% Recombination, or crossing over, is the event in which blocks of genes are exchanged between chromosomes during meiosis. The process involves breakage of two DNA helices and the subsequent exchange. It is generally accepted that unusual DNA structures are formed during recombination. This proposal is directed toward understanding how these unusual DNA structures are recognized and resolved.
