COMPARISON OF THE MAJOR OUTER-MEMBRANE PROTEIN (MOMP) GENE OF MOUSE PNEUMONITIS (MOPN) AND HAMSTER SFPD STRAINS OF CHLAMYDIA-TRACHOMATIS WITH OTHER CHLAMYDIA STRAINS

Restriction fragments containing the major outer-membrane protein (MOM P) gene from two nonhuman (rodent) strains of Chlamydia trachomatis, t he mouse pneumonitis (MoPn) strain and the SFPD strain isolated from h amsters with transmissible proliferative ileitis, were cloned and sequ enced. The MOMP genes of both MoPn and SFPD encode an identical 22-ami no acid leader peptide and mature polypeptides of 365 and 382 amino ac ids, respectively. Alignment of the MOMP genes of the two rodent strai ns revealed 91% identity. By comparison with other known chlamydial MO MP gene sequences, there was 80%-83% identity with human biovars strai ns of C. trachomatis, and there was 69%-70% identity with C. psittaci and C. pneumoniae strains. The main differences in these sequences wer e clustered into four variable domains. A minimum-length evolutionary tree was constructed on the basis of the MOMP gene variable positions by using PIMA package software. The minimum mutation distances indicat ed that (i) the MOMP genes of all chlamydial strains may have evolved from a common ancestor; (ii) all the strains of C. trachomatis compose one of the subtrees, and strains of C. psittaci and C. pneumoniae com pose the other subtree; and (iii) in the C. trachomatis subtree, the h uman and the rodent strains are divided into two clusters. The branchi ng pattern of this evolutionary tree is generally consistent with curr ent classification based on serological, morphological, and other biol ogical characteristics.