UNIVERSAL MINICIRCLE SEQUENCE BINDING-PROTEIN, A CCHC-TYPE ZINC-FINGER PROTEIN THAT BINDS THE UNIVERSAL MINICIRCLE SEQUENCE OF TRYPANOSOMATIDS - PURIFICATION AND CHARACTERIZATION

Replication of kinetoplast DNA minicircles of trypanosomatids initiate s at a conserved 12-nucleotide sequence, termed the universal minicirc le sequence (UMS, 5'-GGGGTTGGTGTA-3'). A single-stranded nucleic acid binding protein that binds specifically to this origin-associated sequ ence was purified to apparent homogeneity from Crithidia fasciculata c ell extracts. This UMS-binding protein (UMSBP) is a dimer of 27.4 kDa with a 13.7-kDa protomer. UMSBP binds single-stranded DNA as well as s ingle-stranded RNA but not double-stranded or four-stranded DNA struct ures. Stoichiometry analysis indicates the binding of UMSBP as a prote in dimer to the UMS site. The five CCHC-type zinc finger motifs of UMS BP, predicted from its cDNA sequence, are similar to the CCHC motifs f ound in retroviral Gag polyproteins. The remarkable conservation of th is motif in a family of proteins found in eukaryotic organisms from ye ast and protozoa to mammals is discussed.