INCREASED LEVELS OF POLYADENYLATED HISTONE H2B MESSENGER-RNA ACCUMULATE DURING ENTAMOEBA-INVADENS CYST FORMATION

We have isolated cDNA clones of a member of the histone H2B protein fa mily by differential screening of an Entamoeba invadens cDNA library w ith cDNA probes from vegetatively growing or encysting parasites. The cDNA clones reveal two polyadenylation sites, 26 nucleotides and 31 nu cleotides downstream from the stop codon. RNA species recognized by E. invadens histone H2B clones are found at increased levels during cyst formation. Histone H2B RNA could be detected in both the poly(A)(+) a nd poly(A)(-) RNA fractions, with stage-specific differences in the st eady state levels of the two RNAs: trophozoites contain predominantly the poly(A)(-) RNA, while encysting parasites express predominantly th e poly(A)(+) RNA. Southern blot analysis suggests that both forms are transcribed from a single copy gene.