The full-length gene that encodes the light chain variable regions of an idiotypically related group of human IgM kappa rheumatoid factors (RFs) has been cloned and sequenced. The deduced amino acid sequence is identical to four separate RF proteins. These results prove that genes capable of encoding human anti-IgG autoantibody light chains without any somatic mutation are present in the kappa gene repertoire of normal people.

The undifferentiated embryonal carcinoma (EC) cell line PCC4 aza 1 was infected with a selectable amphotropic retrovirus. Although EC cells are generally refractory to retroviral gene expression, we found that approximately 1 of 5,000-10,000 recombinant proviruses was transcribed in these cells. Cells containing an active recombinant provirus were cloned and expanded. Nucleic acid analysis revealed approximately one intact provirus per cell. Viral RNA levels were different for each cell clone examined [between 0.05% and 0.5% of the poly(A)+ RNA], and transcription was initiated and terminated in the long terminal repeats as in permissive differentiated cells. The cells retained an undifferentiated phenotype and remained positive for stage-specific embryonic antigen 1 and negative for H-2 surface antigens. The cells retained the block to the expression of other proviruses integrated at other chromosomal locations. The data suggest that a cisacting genetic element, at or near the chromosomal site of integration, or mutations in the viral control elements themselves may be responsible for provirus expression in these cells.The ability to transfer cloned genes into preimplantation embryos has opened the way for the study of gene expression in the maturing organism. Unfortunately, much of the early work has suggested that many cloned genes do not carry the information necessary to guarantee their proper expression during differentiation (1-4). Similarly, the expression of cloned retroviral genes introduced into preimplantation embryos seems to depend on the chromosomal site of integration (5). Most retroviral genomes introduced in this way are not expressed at all and become highly methylated (5).Undifferentiated embryonal carcinoma (EC) cells provide a useful model system for studying early gene expression. As in early embryos, retroviral genomes are not expressed in undifferentiated EC cells (6-8). Yet EC cells present no block to viral penetration, reverse transcription, or viral DNA integration (9, 10). Although newly integrated proviruses become methylated in EC cells (10), this modification occurs several days after integration, suggesting that methylation may be a result, not a cause, of provirus inactivity (11,12). Thus, a provirus that has integrated into a transcriptionally active region of a chromosome might escape inactivation-at least while that region remained transcriptionally active.With this in mind, we infected undifferentiated EC cells with a selectable recombinant retrovirus (13) Fig. 1).This recombinant genome replicates in the presence of amphotropic helper virus. Reverse transcriptase levels were measured as described (16).Infections. Culture supernatant containing defective cistorneo particles was adjusted to 8 ,ug of Polybrene per ml and passed through a 0.45-gm filter. The filtrate was added to plates of NIH 3T3 or PCC4 target cells for 2 hr. The plates were then supplemented with regular culture media. Certain PCC4 lines containing cistomeo proviruses were superinfected with amphotr...

The contribution of germ-line variable regions to autoantibody formation in humans is poorly understood. To study the gene structure of a human autoantibody, chronic lymphatic leukemia (CLL) cells from a patient with an IgM anti-IgG (rheumatoid factor, RF) paraprotein were utilized. The rearranged immunoglobulin gene encoding the K light chain for the RF was cloned, and the nucleic acid sequence of its variable region was determined. As demonstrated by Southern blot analysis using a Kjoining-region probe, the CLL cells, stable CLL-WIL2-729-HF2 RF-secreting hybridomas, and the cloned light-chain gene all had an identical restriction fragment containing the rearranged light-chain gene. The CLL RF light chains reacted weakly with an antipeptide antibody against a primary structure-dependent idiotype present on the light chains of the majority of IgM RF paraproteins. The nucleotide and predicted amino acid sequences of the CLL light-chain gene place it in the K Im variable-region subgroup, and a comparison to known RF paraproteins reveals marked homology to the light-chain amino acid sequence of the IgM RF paraprotein Pom. Both Pom and the CLL light chain appear to identify a second K Ill gene or gene group that is able to encode RF paraprotein light chains.