CONSERVATION AND VARIABILITY IN ARCHAEA - PROTEIN ANTIGENS WITH TANDEM REPEATS ENCODED BY A CLUSTER OF GENES WITH COMMON MOTIFS IN METHANOSARCINA-MAZEI S-6

Three open reading frames, orf492, orf375 and orf783, were identified in a 5.9-kb DNA fragment from the genome of Methanosarcina mazei S-6 t hat code for proteins recognized by antibodies against cell-surface an tigens. The deduced amino-acid (aa) sequences of orfs492 and 375, i.e. , ORF492 and ORF375, contain seven and four copies of an approx, 42-aa repeat, respectively. The aa sequence of ORF783 contains nine copies of an approx. 85-aa repeat, one of which is also present once in each of the first two ORFs. The organization of the repeats is similar to t hat of some Gram(+) cell-wall-associated proteins. Comparative analyse s of aa sequences, compositions and hydropathy profiles of the archaea l ORFs showed similarity with surface (S-) layer and outer-membrane pr oteins of Bacteria and Archaea.