A NUCLEAR-ENCODED CHLOROPLAST RNP-80 PROTEIN FROM BEAN BINDS TO A THYMINE-RICH SEQUENCE OF SINGLE-STRANDED-DNA

A cDNA encoding a chloroplast homolog of RNP-80, designated bean-RNP1, has been isolated from a library constructed from bean cotyledon RNA. The protein contains a chloroplast transit peptide sequence, an acidi c domain, and two RNP-80 domains. Gel mobility shift assays with a pur ified fusion proteins from Escherichia coli demonstrated that the prot ein binds specifically to thymine-rich single-stranded DNA. The protei n interaction with double-stranded DNA was not detectable, S1 nuclease footprinting assays demonstrated that the protein protects a 21-nucle otide thymine-rich sequence from S1 nuclease digestion, In addition, h ypersensitive sites were generated upstream of the binding site, Impli cations of these findings for the possible in vivo function of bean RN P1 are discussed.