d Address for correspondence: James A. Kennison, Bldg. 6B, Room 3B-331, NIH, Bethesda, MD 20892-2785. Tel: (301) 496-8399; fax: (301) 496-0243; e-mail:
jkl5o@nih.gov
The
Sex combs reduced gene of the Antennapedia complex specifies
the identities of the anterior thoracic and posterior head segments,
including the primordium of the larval salivary gland. The
Sex combs reduced transcription unit spans over 30 kb of genomic
DNA, with another 40 kb of upstream cis-regulatory sequences.
The pattern of
Sex combs reduced transcription is set in the
early embryo by the segmentation genes and is then maintained
by two competing sets of proteins, the Polycomb group and the
trithorax group. One of the trithorax group genes required for
activation, the
brahma gene, encodes an evolutionarily conserved
DNA-stimulated ATPase that is part of a large protein complex.
This complex facilitates the action of sequence-specific, DNA-binding
proteins in regulating target genes, possibly by altering chromatin
structure.
