ABSTRACT
The polytene male X chromosome of D. melanogaster, has a unique morphology, which is correlated with the property of increased transcription of the sex-linked genes of the male X chromosome. This ensures equalization of X-linked gene products between males (XY) and females (XX). Till date, an invariable correlation between the structure and transcription of the male X chromosome has been reported. However, the strain In(1)BM2(reinverted) of D. melanogaster presents a caveat to this invariable correlation. In this strain, although the male X chromosome appears puffy and diffuse, the transcription remains at the wild type level. This observation suggests the perturbation in the function of a regulator that controls the structure of the male X chromosome. In this report the response of the strain to butyrate, an inhibitor of histone deacetylase, has been studied, with specific reference to development, sex ratio and chromosome morphology of the strain. Two important conclusions arise from these experiments : (a) exposure to butyrate has more severe consequences on the development of the mutant strain and on the survival of females. (b) rearing on butyrate induced a temporal series of structural alteration of the polytene chromosome of the wild type, with the male X chromosome being most vulnerable to structural changes. The butyrate-interaction of In(1)BM2(reinverted) together with our current biochemical analyses of a chromosome coiling protein recovered from this strain, provide data for a working hypothesis explaining the sex and chromosome specific alteration of the structure of the male X chromosome of In(1)BM2(reinverted).