THE RNHB GENE ENCODING RNASE HII OF STREPTOCOCCUS-PNEUMONIAE AND EVIDENCE OF CONSERVED MOTIFS IN EUKARYOTIC GENES

A single RNase H enzyme was detected in extracts of Streptococcus pneu moniae. The gene encoding this enzyme mas cloned and expressed in Esch erichia coli, as demonstrated by its ability to complement a double-mu tant rnhA recC strain, Sequence analysis of the cloned DNA revealed an open reading frame of 290 codons that encodes a polypeptide of 31.9 k Da. The predicted protein exhibits a low level of homology (19% identi ty of amino acid residues) to RNase HII encoded by rnhB of E. coli, Id entification of the S. pneumoniae RNase HII translation start site by amino-terminal sequencing of the protein and of mRNA start sites by pr imer extension with reverse transcriptase showed that the major transc ript encoding rnhB begins at the protein start site. Comparison of the S. pneumoniae and E. coli RNase HII sequences and sequences of other, putative bacterial rnhB gene products surmised from sequencing data r evealed three conserved motifs. Use of these motifs to search for homo logous genes in eucaryotes demonstrated the presence of rnhB genes in a yeast and a roundworm. Partial rnhB gene sequences were detected amo ng expressed sequences of mouse and human cells. From these data, it a ppears that RNase HII is universally present in living cells.