ISOLATION AND CHARACTERIZATION OF A MITOGEN CHARACTERISTIC OF GROUP-ASTREPTOCOCCI (STREPTOCOCCUS-PYOGENES)

It has been supposed for many years that group A streptococci may elab orate more than the three well known erythrogenic toxins A, B or C (ET A, ETB, ETC). The analysis of the culture supernatant of streptococcal strain 27297 carrying neither genes for ETA nor ETC revealed mitogeni c activity at pH 7.3 in isoelectric focusing. This mitogen of strain 2 7297 was purified by hydrophobic adsorption to Phenyl-Sepharose follow ing FPLC chromatography on a Mono S column resulting in two proteins w ith mitogenic activity called AX and BX, respectively. Both differed i n only one aminoterminal residue. The mitogenic activity of BX lacking one aminoterminal arginine was found to be about 100 times higher tha n that of AX. The aminoterminus of BX does not correspond to a predict able cleavage site for signal peptidase. We assume that BX was produce d after translation by cleavage of the mature protein or the AX molecu le with streptococcal proteinase (ETB) or an arginylaminopeptidase whi ch is detectable on whole cells. The purified proteins BX and AX showe d molecular weights of about 27 kDa in SDS electrophoresis and isoelec tric points of 8.3 (AX) and 7.3 (BX) in isoelectric focusing, respecti vely. Both proteins were produced by practically all group A strains t ested but not by groups B, C, G or H streptococci. Therefore, AX or BX seem to be proteins characteristic of group A streptococci.