trithorax and the regulation of homeotic gene expression in Drosophila: a historical perspective.

Animals homozygous for a spontaneously arising allele of the trithorax (trx) gene exhibit highly variegated homoeotic transformations of their thoracic and abdominal segments. This paper retraces the sometimes tortuous history of the analysis of trx function, from the fortuitous recovery of the first trx allele, to the present understanding that trx encodes a highly conserved chromatin binding protein that is required to maintain the expression of the Antennapedia and Bithorax complex genes.