Inverse complementary homologues of short cysteine signatures

Inversions of short genomic sequences may play a central role in the generation of protein complexity. We report here the existence of an heterogeneous group of proteins (the trefoil precursors MUC-1 and MUA-1, six preproendothelins, and five classes of zinc finger knot proteins) having both cysteine signatures (Cs) and their inverse complementary sequences (Cs) in the same polypeptide chain. We have also found cases in which the (Cs) of a given signature is not present in the same protein, but elsewhere. TGEKPYK, a cysteine-free motif of the human transcription factor, Krab, coexists with its inverse complementary sequence in 31 proteins; the inverse complementary alone is present in a great number of proteins. Our findings suggest that short DNA inversions are a widespread feature of the genome.