Two 1.5-kb macronuclear chromosomes bearing histone H2B genes from the
ciliated protozoan Euplotes crassus were cloned and sequenced. Althou
gh the noncoding sequences on these macronuclear chromosomes are very
different, the genes encode an identical 113-aa histone H2B protein th
at has a shortened N-terminus and a highly conserved C-terminus relati
ve to histone H2B proteins in other organisms. Primer extension was us
ed to determine the transcription start points. Northern analysis show
s that the abundance of H2B mRNA changes relative to DNA replication p
eriods during the sexual phase of the life cycle. Analysis of 3' RACE
products indicates that the H2B genes are coexpressed. (C) 1997 Elsevi
er Science B.V.