GENETIC ORGANIZATION OF THE STREPTOKINASE REGION OF THE STREPTOCOCCUS-EQUISIMILIS H46A CHROMOSOME

The complete nucleotide sequences of four genes and one open reading f rame (ORF1) adjacent to the streptokinase gene, skc, from Streptococcu s equisimilis H46A were determined. These genes are encoded on the opp osite DNA strand to skc and are arranged as follows: dexB-abc-lrp-skc- ORF1-rel. The dexB gene, coding for an a-glucosidase (M(r) 61733), and abc, encoding an ABC transporter (M(r) 42080), are similar to the dex B and msmK genes, respectively, from the multiple sugar metabolism ope ron of S. mutans. The lrp gene specifies a leucine-rich protein (M(r) 32302) that has a leucine-zipper motif at its C-terminus. The function of the Lrp protein is not known but appeared to be detrimental when o verexpressed in Escherichia coli. Although lrp appears not to be an es sential gene, as judged by plasmid insertion mutagenesis, it is conser ved in all streptococcal strains carrying a streptokinase gene. The re l gene showed significant homology to the E. coli relA and spoT genes involved in the stringent response to amino acid deprivation. Multiple alignment of the amino acid sequences of Rel (M(r) 83913), RelA and S poT revealed 59.4 % homology of the primary structures. Northern hybri diziation analyses of the genes in the skc region showed skc to be tra nscribed most abundantly. In addition to transcripts for skc, monocist ronic mRNAs were detected for all three genes divergently transcribed from skc. Although there was also some read-through transcription from lrp into abc, and from abc into dexB, the transcription pattern sugge sts a high degree of transcriptional and functional independence not o nly of skc but also abc and dexB. Prominent structural features in int ergenic regions included a static DNA bending locus located upstream a nd a putative bidirectional transcription terminator downstream of skc .