SEQUENCE, CODON USAGE AND CYSTEINE PERIODICITY OF THE SERH1 GENE AND IN THE ENCODED SURFACE PROTEIN OF TETRAHYMENA-THERMOPHILA

The temperature-regulated SerH1 gene coding for an immunodominant surf ace glycoprotein (i-Ag H1) of Tetrahymena thermophila has been sequenc ed. The gene is reproducibly rearranged during macronuclear developmen t and steady state mRNA levels are present at <36 degrees C. The deduc ed i-Ag H1 amino acid (aa) sequence is rich in Ser, Thr and Cys; and c ontains three periods each consisting of 85 aa punctuated by eight Cys with the general formula, CX(6)CX(17)CX(2)CX(18)CX(2)CX(11)CX(2)CX(19 ) (where X = any aa). Such Cys periodicity is common to ciliate i-Ag. Codon usage in Tt, Paramecium primaurelia and P. tetraurelia i-Ag enco ding genes is similar, with approx. 80% A+T in the 3' position which i s in marked contrast to the approx. 54% 3' A+T in other ciliate genes.