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 degrees 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, CX6CX17CX2CX18CX2CX11CX2CX19 (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.