ASSOCIATION OF SARFH (SARCOMA-ASSOCIATED RNA-BINDING FLY HOMOLOG) WITH REGIONS OF CHROMATIN TRANSCRIBED BY RNA-POLYMERASE-II

Many oncogenes associated with human sarcomas are composed of a fusion between transcription factors and the N-terminal portions of two simi lar RNA-binding proteins, TLS and EWS. Though the oncogenic fusion pro teins lack the RNA binding domain and do not bind RNA, the contributio n from the N-terminal portion of the RNA-binding protein is essential for their transforming activity. TLS and EWS associate in vivo with RN A polymerase II (Pol II) transcripts. To learn more about the target g ene specificity of this interaction, the localization of a Drosophila melanogaster protein that has extensive sequence identity to the C-ter minal RNA-binding portions of TLS and EWS was studied in preparations of Drosophila polytene nuclei. cDNA clones encoding the full-length Dr osophila TLS-EWS homolog, SARFH (stands for sarcoma associated RNA-bin ding fly homolog), were isolated. Functional similarity to TLS and EWS was revealed by the association of SARFH with Pol II transcripts in m ammalian cells and by the ability of SARFH to elicit homologous down-r egulation of the levels of the mammalian proteins. The SARFH gene is e xpressed in the developing Drosophila embryo from the earliest stages of cellularization and is subsequently found in many cell types. In pr eparations of polytene chromosomes from salivary gland nuclei, SARFH a ntibodies recognize their target associated with the majority of activ e transcription units, revealed by colocalization with the phosphoryla ted form of RNA Pol II. We conclude that SARFH and, by homology, EWS a nd TLS participate in a function common to the expression of most gene s transcribed by RNA Pol II.