The goal of this proposal is to contribute to the eventual understanding of how reverse transcriptase participates in the generation, in germ line cells, of Alu-like elements and processed genes. One group of aims is to pursue the observation that in the endogenous RNA-directd DNA snythesis of melittin-disrupted quail-grown retrovirus, the cellular 7S-L RNA is reverse transcribed using a tRNA-sized primer to generate a major discrete 130b species of DNA. This observation is doubly tantalizing. Firstly, it suggests an analogy to the early events in the reverse transcription of the avian retroviral genome in whch tRNA.trp is used as primer for the transcription of a specific 101b species from the 5'-end of the RNA genome. Secondly, it suggests that the observed reverse transcription of 7S-L RNA may be a step in the process by which the DNA of eucaryotic cells has accumulated multiple copies of what are referred to as Alu-like elements. This suggestion is made because such elements are fequently about 130b long and show significant sequence-relatedness to the 5'-terminus of the 7S-L RNA. The studies proposed will therefore test for 7S-L RNA the hypothesis of others that reverse transcription of cellular RNA's may be involved not only in the generation and transmission of Alu-like elements but also of certain pseudogenes, processed genes and gene conversion events. Such phenomena are all analogous to the formation of endogenous retrovirus-like DNA elements in that they could require, albeit rarely, reverse transcription events to take place in germ line cells. For this reason the second group of aims are directed at potential sources of reverse transcriptase in the quail. By high stringency hybridization the quail is free of DNA related to the reverse transcriptase of avian leukosis virus. However, with lowered stringency it has been possible to detect and clone in a lambda vector sequences that are related to the retroviral polymerase gene. The structure of these sequences will be determined and their expression as RNA assayed in quail embryonic tissues. The sequences will also be tested for relationship to those of the retrovirus-like particles, reportedly released from embryonic quail tissues, in the studies of Hofschneider and coworkers.
