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 surface glycoprotein (i-Ag H1) of Tetrahymena thermophila has been sequenced. The gene is reproducibly rearranged during macronuclear development and steady state mRNA levels are present at < 36° C. The deduced i-Ag H1 amino acid (aa) sequence is rich in Ser, Thr and Cys, and contains three periods each consisting of 85 aa punctuated by eight Cys with the general formula, CX 6CX 17CX 2CX 18CX 2CX 11CX 2CX 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 encoding genes is similar, with approx. 80% A + T in the 3′ position which is in marked contrast to the approx. 54% 3′ A + T in other ciliate genes.