Interspecies structural diversity among chlamydial genes encoding histone H1

Abstract

Recently, a eukaryotic histone H1-like protein has been detected in Chlamydia trachomatis serovar L 2 [Hackstadt et al., Proc. Natl. Acad. Sci. USA 88 (1991) 3937–3941; Tao et al., J. Bacteriol. 173 (1991) 2818–2822]. We have cloned the corresponding gene from C. trachomatis serovar J and the Chlamydia psittaci strain mn. Sequencing demonstrated absolute gene identity between the two C. trachomatis serovars L 2 and J, but divergence in the C. psittaci strain mn. These differences resulted in altered aa residues (in particular no cysteines) and a smaller molecular mass for H1 from C. psittaci strain mn. The amino acid (aa) sequence comparisons with other histone proteins show best alignment to sea urchin H1, notably in the C terminus, for both C. trachomatis and C. psitacci histones. Chlamydial interspecies aa homology, however, is most conserved at the N terminus, suggestive of a bi-functional role for these unique histone proteins.