tokens: To test this hypothesis , light-chain gene structure was examined in pre-B cells transformed by temperature-sensitive mutants of the Abelson virus and in derivatives that survive at the nonpermissive temperature because they express a human BCL-2 gene .
folded_tokens: to test this hypothesis , light-chain gene structure was examined in pre-b cells transformed by temperature-sensitive mutants of the abelson virus and in derivatives that survive at the nonpermissive temperature because they express a human bcl-2 gene .
labels: O O O O O B-DNA_domain_or_region I-DNA_domain_or_region I-DNA_domain_or_region O O O B-cell_line I-cell_line O O B-virus I-virus O O B-virus I-virus O O O O O O O O O O O O O B-DNA_domain_or_region I-DNA_domain_or_region I-DNA_domain_or_region O