The mechanisms by which ribosomal protein gene expression is controlled will be examined through the use of cloned probes. In particular the mechanism by which the temperature sensitive RNA mutations affect the levels of ribosomal protein mRNAs will be examined. Recent work has suggested that this mechanism is post-transcriptional and additional confirmatory experiments will be pursued as well as experiments to further define the specific lesion of the RNA2 locus. The possibility that the mRNAs are controlled by an autogeneous regulation will also be explored. Sequencing of a number of ribosomal protein structural genes as well as the 5' flanking regions will be continued in order to: (1) see if 5' flanking regions manifest any homology and (2) to prove that introns are present in the ribosomal protein genes and that precursors contain these introns whereas the mature mRNAs do not. Studies to find additional Drosophila ribosomal protein genes will continue. In addition, the sequence organization surrounding our known cloned ribosomal protein gene will be analyzed in order to further define the nature and significance of all of the transcripts on this phage and to see if any additional ribosomal protein genes are present.