STRUCTURAL AND FUNCTIONAL-PROPERTIES OF THE HSP16.4-BEARING PLASMID PER341 IN STREPTOCOCCUS-THERMOPHILUS

The plasmid pER341 (2798 bp) of Streptococcus thermophilus ST134 was s equenced and its open reading frame (ORF) regions were characterized. Analysis of nucleotide sequences showed the putative translation produ ct of ORF1 (rep) sharing a high level of homology with replication pro teins of several small plasmids present in lactic acid bacteria and st aphylococci. This and homology of regions of plus-strand (ORI) and min us-strand (ssoA) origin of replication with pC194-class plasmids indic ated that pER341 replicates by the rolling-circle mechanism. ORF2 corr esponded to a putative hsp gene that apparently encodes Hsp16.4, a 142 -amino-acid heat stress protein. Hsp16.4 shared significant identity w ith other small, 18-kDa-class heat stress proteins from prokaryotic an d eukaryotic sources. Hsp16.4 is apparently the first plasmidborne low -molecular-weight heat stress protein reported in dairy fermentation b acteria with a potential role in temperature-regulated functions in S. thermophilus.