CONSERVED AND VARIABLE REGIONS IN PROTEIN ARP, THE IGA RECEPTOR OF STREPTOCOCCUS-PYOGENES

The streptococcal M protein family, a number of cell surface molecules that interact with the human immune system, can be divided into two m ajor classes, A and C, characterized by different types of repeats in the central part of the molecule. Class A and class C molecules are kn own to have a variable N-terminal region and a more conserved C-termin al region, but little is known about the mechanisms that give rise to this structural variation. In this report, we show that two variants o f protein Arp, an IgA receptor in class C of the M protein family, hav e virtually identical signal sequences and C-terminal halves, but unre lated N-terminal sequences. Comparison of the sequences of the two gen es and their flanking regions also demonstrates the presence of well-d efined variable and conserved regions. Our results strongly suggest th at the N-terminal sequence variation between the two variants of prote in Arp was generated through an intergenic recombination event, rather than through intragenic recombination or accumulation of mutations.