A Yersinia pestis-specific DNA fragment encodes temperature-dependent coagulase and fibrinolysin associated phenotypes

The effect of temperature on coagulase and fibrinolysin expression (Pla) by Yersinia pestis has been implicated in the transmission of plague by fleas. In an attempt to improve our understanding of this process, we have cloned, sequenced and characterized the gene encoding the Pla phenotypes in Y. pestis, and examined its temperature-dependent regulation. The coding region for this gene overlaps a 900bp Y. pestis-specific DNA fragment that we have previously shown to be capable of detecting plague bacilli in fleas. The pla gene contains a single open reading frame encoding 312 amino acids with a predicted molecular weight of 34.7 kD and a putative signal sequence of 20 amino acids. This coding region appears to be sufficient for both coagulase and fibrinolytic activities. In Y. pestis, modulation between coagulase and fibrinolytic activities is temperature-dependent: coagulase activity is most evident at temperatures below 30 degrees C but fibrinolytic activity increases with higher temperatures (greater than 30 degrees C), regardless of the temperature at which the bacteria are grown. Our results lead us to believe that this regulation occurs post-translationally. It is possible that the alternative forms of the Pla protein are essential to 'flea blockage' and subsequent transmission of the plague bacillus to animals.