It enables males to double the expression of the genes in their single X chromosome - a process called dosage compensation - by binding to the body of those genes together with a protein called MOF.
Scientists have identified a novel protein complex that regulates around 4,000 genes in the fruit fly Drosophila and likely plays an important role in mammals, too.
"This new complex seems to be one of the major regulatory complexes both in Drosophila and in mammals," says Asifa Akhtar, former EMBL group leader and now at the Max-Planck Institute of Immunobiology in Freiburg, Germany.
It enables males to double the expression of the genes in their single X chromosome - a process called dosage compensation - by binding to the body of those genes together with a protein called MOF. Thus, male flies are able to compensate for the fact that they have only one X chromosome, while females have two. But MOF leads a double life: it also binds to the promoter regions of genes on all chromosomes, in both sexes.
Akhtar and colleagues named it Non-Specific Lethal (NSL), in contrast to a previously known complex called Male-Specific Lethal (MSL).
If the complex interacts with MSL instead, it binds to genes on the males' X-chromosome, playing its role in dosage compensation. Interestingly, NSL indirectly drives this aspect of MOF function too, by acting together with MOF to turn on the genes whose output will then be increased by dosage compensation.
"These proteins have been conserved throughout evolution - they exist not only in fruit flies but in mammals too, meaning that everything we have discovered in flies has implications for humans and other mammals, which we'd like to investigate next," Akhtar concludes.