Transcription of chromatin-packaged genes involves highly regulated ch
anges in nucleosomal structure that control DNA accessibility. Two sys
tems that facilitate these changes are ATP-dependent chromatin remodel
ing complexes and enzymatic complexes which control histone acetylatio
n and deacetylation. Recent studies provide insight on the role of the
se remodeling machines and specific transcription factors in the expre
ssion of viral, inducible, and tissue-restricted genes. (C) Current Bi
ology Ltd ISSN 0959-437X.