Chromatin structures of goat and sheep β-lactoglobulin gene differ

Different levels of the major milk protein β-lactoglobulin are found in evolutionarily related ruminant species: with sheep milk containing as much as three times the concentration in goat milk. In an attempt to understand why these differences exist, we have characterised, using DNaseI as a probe of structure, the chromatin surrounding the goat β-lactoglobulin promoter and compared it to that of the sheep homologue. The goat gene displays a mammary-specific chromatin pattern, which is reformed on expressing goat β-lactoglobulin transgenes. This implies that this chromatin structure is sequence dependent and suggests that it plays a role in regulating β-lactoglobulin gene expression. This pattern differs from that seen on the ovine β-lactoglobulin gene in lactating sheep mammary chromatin. Thus, even between highly related species, the transcriptional mechanisms regulating activity of a gene can differ.