Derivatives of the mu-producing Abelson line P8 have been analyzed for L chain gene rearrangements. Two of seven clones studied assembled their V lambda genes while growing in culture. V lambda gene rearrangements occurred only in those Abelson subclones that either were rearranging or had rearranged their recombining sequence (RS) element on both Ig kappa alleles. Our data suggest that (a) RS rearrangements are preferentially initiated in kappa- pre-B cells; and (b) the deletion or inactivation of sequences lying between J kappa and RS is a requirement for the activation of the Ig lambda locus.

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