Transcription of mouse kappa chain genes: implications for allelic exclusion.

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Abstract
The nuclear RNA from a large variety of .kappa.-producing plasmacytomas was size fractionated and analyzed with a series of cloned probes representing sequences encoding variable (V), joining (J) and constant (C) regions and selected intervening sequences. All of the plasmacytomas produce a nuclear RNA component that contains V.kappa. and C.kappa. sequences and the intervening sequence between J.kappa. and C.kappa.. The nuclear RNA has a distinctive size depending on which of the 4 segments is expressed (i.e., is present in the secreted .kappa. chain). These RNA are the precursors of .kappa. mRNA, which are transcribed from productively rearranged C.kappa. genes. Half of the plasmacytomas examined produce, in addition to .kappa. mRNA precursor, a discrete component of about 8.4 kbases that contains C.kappa. and upstream flanking sequences but lacks the expressed V region sequence. The ability to produce this component is always associated with the persistence in the tumor genome of an unrearranged (germline) J.kappa.-C.kappa. region. In tumors rearranged at both .kappa. loci the nonproductive allele is either transcriptionally silent or, in a minority of cases, transcribed and processed into a fragment MRNA lacking V region sequences. Allelic exclusion can apparently be effected at several levels of gene expression. Some insight into the relative contributions of the V and C gene elements to this expression were discussed.