An RNA polymerase III transcription unit located in the upstream control regions of the human proliferating-cell nucleolar protein p120 gene is transcribed in vitro and in vivo

An RNA polymerase III (Pol LII) transcription unit containing homology to h ighly repeated Alu sequences was identified in the upstream flanking sequen ces of the gene for the human proliferating-cell nucleolar antigen p120. Wh en transcribed in vitro, this Pol III unit produced three RNA transcripts, designated by nucleotide length as T150, T385 and T635; RNA transcript T635 was the most abundant accounting for over 90%. The transcription initiates at nucleotide -729 of the human p120 promoter and proceeds in the opposite orientation to the p120 gene transcription. Northern blot analysis and cDN A cloning followed by sequencing showed the presence of the T635 RNA in HeL a cells, indicating that this Pol III transcription unit is functional and transcribed in vivo. Disruption of this Pol III transcription unit by delet ion of the Box A residues (-733 to -744) resulted in a sixfold reduction of the p120 gene transcription. A possible role for this Pol III transcriptio n unit in p120 gene transcription is discussed.