A TRYPANOSOMAL CCHC-TYPE ZINC-FINGER PROTEIN WHICH BINDS THE CONSERVED UNIVERSAL SEQUENCE OF KINETOPLAST DNA MINICIRCLES - ISOLATION AND ANALYSIS OF THE COMPLETE CDNA FROM CRITHIDIA-FASCICULATA

Replication of the kinetoplast DNA minicircle light strand initiates a t a highly conserved 12-Nucleotide sequence, termed the universal mini circle sequence. A Crithidia fasciculata single-stranded DNA-binding p rotein interacts specifically with the guanine-rich heavy strand of th is origin-associated sequence (Y. Tzfati, H. Abeliovich, 1. Kapeller, and J. Shlomai, Proc. Natl. Acad. Sci. USA 89:6891-6895, 1992). Using the universal minicircle sequence heavy-strand probe to screen a C. fa sciculata cDNA expression library, we have isolated two overlapping cD NA clones encoding the trypanosomatid universal minicircle sequence-bi nding protein. The complete cDNA sequence defines an open reading fram e encoding a 116-amino-acid polypeptide chain consisting of five repet itions of a CCHC zinc finger motif. A significant similarity is found between this universal minicircle sequence-binding protein and two oth er single-stranded DNA-binding proteins identified in humans and in Le ishmania major. All three proteins bind specifically to single-strande d guanine-rich DNA ligands. Partial amino acid sequence of the endogen ous protein, purified to homogeneity from C. fasciculata, was identica l to that deduced from the cDNA nucleotide sequence. DNA-binding chara cteristics of the cDNA-encoded fusion protein expressed in bacteria we re identical to those of the endogenous C. fasciculata protein. Hybrid ization analyses reveal that the gene encoding the minicircle origin-b inding protein is nuclear and may occur in the C. fasciculata chromoso me as a cluster of several structural genes.