BLOCK IN NUCLEAR-LOCALIZATION OF PERIOD PROTEIN BY A 2ND CLOCK MUTATION, TIMELESS

In wild-type Drosophila, the period protein (PER) is found in nuclei o f the eyes and brain, and PER immunoreactivity oscillates with a circa dian rhythm. The studies described here indicate that the nuclear loca lization of PER is blocked by timeless (tim), a second chromosome muta tion that, like per null mutations, abolishes circadian rhythms. PER f usion proteins without a conserved domain (PAS) and some flanking sequ ences are nuclear in tim mutants. This suggests that a segment of PER inhibits nuclear localization in firn mutants. The tim gene may have a role in establishing rhythms of PER abundance and nuclear localizatio n in wild-type flies.