Differential expression of linker histone variants in Euplotes crassus

Two genes have been cloned from the ciliate Euplotes crassus that encode pr oteins with sequence similarity to the linker histones from a variety of or ganisms. One gene, H1-1, is present on a 1.3-kb macronuclear DNA molecule a nd encodes a 16.2- kDa protein. The second gene, H1-2, is present on a 0.7- kb DNA molecule and encodes an 18.8-kDa protein. Bath HI-I and H1-2 are exp ressed in vegetative cells, but the two genes exhibit very different patter ns of expression during macronuclear development. HI-I transcripts accumula te during conjugation and during the final rounds of DNA amplification. H1- 2 transcripts accumulate after the onset of polytene chromosome formation a nd remain high throughout the remainder of macronuclear development. H1-1 i s the major perchloric-acid-soluble protein from macronuclei. The pattern o f gene expression and the macronuclear location of the H1-1 protein indicat e that H1-1 is the predominant linker histone in vegetative macronuclei. (C ) 1999 Elsevier Science B.V. All rights reserved.