All about abo

Mutation of the Drosphila abnormal oocyte (abo) gene causes a recessive maternal-effect lethality, which can be rescued by specific regions of heterochromatin. In the October 9 Proceedings of the National Academy of Sciences, Berloco et al. report a characterization of the abo protein product and its function (Proc Natl Acad Sci USA 2001, 98:12126-12131). They cloned the abo gene and showed that it encodes a chromosomal protein that binds specifically to the regulatory regions within the histone gene cluster (on the 39E region of polytene chromosomes). Similar proteins were found in Arabidopsis (the DET1 protein), as well as in mouse and man. Chromatin immunoprecipitation experiments demonstrated that Abo binds to the histone gene promoter regions, and abo mutations affected histone expression levels. Deleting the histone cluster rescued the abo maternal-effect defects. The authors conclude that Abo is a negative regulator of histone gene expression.