EXPRESSION STUDIES ON 4 MEMBERS OF THE PMGA MULTIGENE FAMILY IN MYCOPLASMA-GALLISEPTICUM S6

A large family of related genes known as pMGA exists in the avian path ogen Mycoplasma gallisepticum but only a single member of this family was previously found to be expressed in one strain of this bacterium. In this work two unrelated strains of M. gallisepticum were also shown by amino-terminal sequencing to express a unique pMGA polypeptide in both cases. To investigate pMGA gene selection in M. gallisepticum, mR NA expression was analysed in M. gallisepticum strain S6 using reverse transcription-PCR (RI-PCR) and Northern blot techniques with probes f or several members of the pMGA multigene family. It was shown that the pMGA message is 2.2 kb in size and is monocistronic. RT-PCR detected four different pMGA mRNA molecules but their relative yields were sign ificantly affected by magnesium concentration. By quantitative Norther n analysis, the relative abundances of the four pMGA mRNAs in M. galli septicum S6 total RNA was determined:the pMGA1.1 mRNA predominated [1. 88 ng (mu g total RNA)(-1)] but at least three other pMGA genes were f ound to be transcribed but at much lower levels (20 to 40-fold lower). The pMCA1.1 mRNA is expressed at a level five times higher than the t uf gene, known to be one of the most abundantly expressed proteins in the prokaryotic cell. The start point of transcription for pMGA1.1 was determined and probable promoter assigned. From these data it appears likely that transcriptional control plays a major role in the selecti on of pMGA gene expression in the M. gallisepticum cell.