Localization of tRNA genes in the salivary chromosomes of Drosophila by RNA:DNA hybridization.

HE methods for in situ molecular hybridization to nuclei and chromosomes Thave been developed due primarily to the efforts of GALL and PARDUE (1969), PARDUE et al. (1970) and JOHN, BIRNSTIEL and JONES (1969). In theory the procedure permits the use of any fraction of labeled RNA or DNA to locate the site of specific binding in a genome, provided there is enough radioactivity for detection by autoradiography. During o w recent successful hybridization study locating the genes coding for 5s RNA at region 56EF on chromosome 2 (R) in Drosophila melanogaster ( WIMBER and STEFFENSEN 1970), it became apparent that numerous other sites on the salivary chromosomes were labeled due to the binding of [3H]tRNA which was present in the 5s RNA fraction. The present experiments exploit these observations and provide evidence of cytological location of the genes which code for the transfer RNA molecules in Drosophila melanogaster. The analysis of the location of the ["]tRNA:DNA hybrids has been done for the X chromosome and most of chromosome 2, including the entire right arm (2R) and the distal half of the left arm (2L).