Alu and 7SL RNA gene sequences were tested for the potential to regulate 
mammalian cell growth by introducing these sequences into HeLa cells in a 
coupled DEAE-dextran transfection/affinity cell sorting system. Both Alu and 7SL 
RNA genes mediated inhibition of [3H]thymidine and [35S]methionine incorporation 
in recipient cells. In addition, short term growth curves were performed on 
calcium phosphate/DNA cotransfected, affinity-purified cells. This second assay 
revealed that transfected Alu and 7SL RNA can also cause suppression of HeLa 
cell proliferation. To investigate whether transcription or polymerase III (pol 
III) transcription factor binding was required for inhibitory activity, 
mutations were introduced into RNA pol III B block promoter elements in each of 
these genes. Suppression of [3H]thymidine incorporation was dependent on the 
presence of this pol III element in both genes; likewise, 7SL RNA-mediated 
growth suppression required the presence of the pol III B block promoter 
element. The results of this study indicate that Alu and 7SL RNA gene sequences 
interact with cellular factors that are important for HeLa cell proliferation 
and suggest that these pol III-transcribed elements may be involved in the 
regulation of cellular growth.