| In vivo evidence that defects in the transcriptional elongation factors RPB 2 , TFIIS , and SPT 5 enhance upstream poly ( A ) site utilization . ^^^ We identified in yeast several genes that contain internal poly ( A ) sites whose full length mRNA formation is reduced by mutations in RNA polymerase 2 subunit RPB 2 , elongation factor SPT 5 , or TFIIS . ^^^ RPB 2 and SPT 5 defects also promoted the utilization of upstream poly ( A ) sites for genes that contain multiple 3 ' poly ( A ) signaling sequences , supporting a role for elongation in differential poly ( A ) site choice . ^^^ |