Revised nomenclature for Tetrahymena thermophila histone
genes
The histone gene complement of Tetrahymena thermophila
consists of 12 genes encoding 10 histone proteins including an
unusual HI lacking the conserved central hydrophobic domain,
a unique micronucleus specific linker histone that is totally unlike
HI, and an H2A variant (hvl) that is homologous to mammalian
H2A.Z and chicken H2A.F proteins (Table 1). However, as the
sequences have been determined they have been given a variety
of nonstandard names. In particular, the H3 genes were originally
named H3-I and H3-II despite the fact that the partial sequences
predicted identical peptides (21). Since, with this report the
sequences of all 12 known Tetrahymena histone genes have been
determined (10 by our laboratory), we propose standardizing the
histone gene names. Thus, we have named the genes HHO
(histone H-one), MLH (micronuclear linker histone), HTA
(histone H-two-A), HHT (histone H-three), and so on. We have
retained hvl and hv2 as the names of the proteins encoded by
HTA3 and HHT3 for historical reasons. Note that HHT1 and
HHT2, and HHF1 and HHF2, encode identical major H3 and
H4 proteins, respectively.