Can a protein influence the fate of its own coding sequence?: the amino- and carboxyl-terminal regions of H1 histone.

The amino- and carboxyl-terminal regions of H1 histone are afforded an opportunity to bind to their own coding segments. While such binding is of no consequence to the type of H1 histone that is expressed only in terminally differentiated cells (here referred to as H5), the same binding occurring in H1 of proliferating cells might affect the course of evolution of its amino- and carboxyl-terminal regions. With the above in mind, amino acid sequences of H5 from three species were compared with those of H1 from five species. The spherical core was more conserved in H1 than in H5, whereas the amino- and carboxyl-terminal regions of both were hypervariable. A distinct evolutionary pattern, however, was observed only in these regions of H1 but not of H5. Tandem repeats of short palindromes often generated nearly identical long palindromes in distantly related species. Thus, as far as the 37-residue-long amino-terminal region was concerned, the greatest homology was between the rat and human rather than between the rat and the mouse. With regard to the last 25 residues in the carboxyl-terminal region, the greatest homology was between the chicken and the rainbow trout; the next was between the mouse and the trout. Successions of long palindromes populating the amino- and carboxyl-terminal regions of H1 might be the direct consequence of the autologous binding between peptides and their coding sequence.