The Drosophila clock gene per affects intercellular junctional communication.

The per locus of Drosophila has been implicated in the control of behavioural rhythms. In fruitfly embryos and larvae per is expressed in salivary glands. Per mutations have striking effects on intercellular communication in salivary glands: gap junction channels are modulated so that their conductance varies inversely with the period of behavioural rhythms in the mutants. A similar effect on junctional communication in the nervous system may explain how per influences behavioural rhythms.