SIZE AND GENOMIC LOCATION OF THE PMGA MULTIGENE FAMILY OF MYCOPLASMA-GALLISEPTICUM

The pMGA multigene family encodes variant copies of the cell surface h aemagglutinin of Mycoplasma gallisepticum. Quantitative Southern blott ing, using an oligonucleotide probe complementary to a region conserve d in the leader sequence of all known pMGA genes, was used to estimate the number of members of the family in the genome of seven strains of M. gallisepticum. The number of copies estimated to be present in the genome varied from 32 in strain F to 70 in strain R, indicating that the pMGA gene family may be second in size only to the tRNA family amo ng prokaryotes. If all members of the pMGA family are of similar lengt h to those which have been characterized, a minimum of 79 kb (7.7 %) o f the genome of strain S6, 82 kb (8.2 %) of PG31 and 168 kb (16 %) of the genome of strain R is dedicated to encoding variants of the same h aemagglutinin. The GAA repeat motif identified in the intergenic regio n between all characterized pMGA genes appeared to be a feature common to most, if not all, pMGA genes, and furthermore probably exclusive t o them. The genomic locations of members of the pMGA family were deter mined by PFGE and Southern blot hybridization of M. gallisepticum stra in S6. The hybridizing regions were localized to four separate regions on the chromosome. The pMGA genes are likely to be predominantly arra nged as tandem repeats within these regions, similar to the restricted regions for which the genomic sequence has been determined.