MUTATION OF THE GENE FOR THE 2ND-LARGEST SUBUNIT OF RNA-POLYMERASE-I PROLONGS THE PERIOD LENGTH OF THE CIRCADIAN CONIDIATION RHYTHM IN NEUROSPORA-CRASSA

The period length of the circadian conidiation rhythm was examined in a mutant strain of Neurospora crassa, un-18, that is temperature sensi tive for mycelial growth. The un-18 mutant showed a temperature-sensit ive phenotype with respect to both mycelial growth and the period leng th of the conidiation rhythm. Below 22 degrees C, the un-18 mutation d id not affect the period length, but at temperatures between 22 degree s C and 32 degrees C, the period length of the un-18 mutant was simila r to 2 h longer than that of the wild-type strain. The un-18(+) gene w as cloned and was found to encode the second-largest subunit of RNA po lymerase I, which is involved in the synthesis of rRNA. These results indicate that a defect in ribosome synthesis, which must result in a l ower rate of protein synthesis, lengthens the period of the circadian conidiation rhythm in Neurospora.