Immunoglobulin gene organization of ultraviolet-illuminated human lymphoblastoid cell lines producing both IgM and IgG.

We have studied the immunoglobulin gene organization of ultraviolet light (u.v.)-induced variant cells derived from an Epstein-Barr virus-transformed cell line. One variant produced IgG1 and two variants produced both IgM and IgG1 whereas the parental cell line produced IgM. Southern blot analyses of DNAs of these cells revealed a newly rearranged JH fragment in all the variants. The newly rearranged JH fragment also hybridized with the C gamma 1 sequence. The mu and gamma 1 chains produced in the double isotype-producing variants share the same VH sequence. u.v. illumination also induced rearrangement of the C lambda gene in the IgG1-producing variant. The double isotype producers contained the immunoglobulin gene organization and mutation best explained by fusion of the IgG1 producer and the parental IgM producer.