Almost all organisms exhibit ～ 24-h rhythms,or circadian rhythms,in a plentitude of biological processes.These rhythms are driven by endogenous molecular clocks consisting of a series of transcriptional and translational feedback loops.Previously,we have shown that the inner nuclear membrane protein MAN1 regulates this clock and thus the locomotor rhythm in flies,but the mechanism remains unclear.Here,we further confirmed the previous findings and found that knocking down MAN1 in the pacemaker neurons of adult flies is sufficient to lengthen the period of the locomotor rhythm.Molecular analysis revealed that knocking down MAN1 led to reduced mRNA and protein levels of the core clock gene period (per),likely by reducing its transcription.Over-expressing per rescued the long period phenotype caused by MAN1 deficiency whereas per mutation had an epistatic effect on MAN1,indicating that MAN1 sets the pace of the clock by targeting per.