Transcriptional regulation of the Ig kappa gene by promoter-proximal pausing of RNA polymerase II.

Transcriptional regulation can occur at the level of initiation and RNA elongation. We report that the rearranged, nontranscribed Ig kappa gene in the pre-B cell line 70Z/3 harbors a paused RNA polymerase II (pol II) at a position between 45 and 89 bp downstream of the transcription initiation site. LPS, an inducer of NF-kappa B, activated Ig kappa gene transcription by increasing the processivity of pol II. TGF-beta inhibited the LPS-induced transcription of the Ig kappa gene, but not initiation and pausing of pol II. A rearranged copy of the Ig kappa gene was introduced into 70Z/3 cells using an episomal vector system. The episomal Ig kappa was regulated by LPS and TGF-beta like the endogenous gene and established a paused pol II, whereas a construct with a deletion of the intron enhancer and the C region did not establish a paused pol II. Two distinct functions can therefore be assigned to the deleted DNA elements: loading of pol II to its pause site and induction of processive transcription upon LPS stimulation. It had been proposed that somatic hypermutation of Ig genes is connected to transcription. The pause site of pol II described in this work resides upstream of the previously defined 5' boundary of mutator activity at Ig kappa genes. The possible role of pausing of pol II for somatic hypermutation is discussed.