passages.id: split_6_test_2683_passage
passages.type: progene_text
passages.text: Both the authentic alpha4 subunit ( alpha4A ) and the variant with the heptapeptide insertion ( alpha4B ) were readily secreted as laminin - 8 trimers ( alpha4Abeta1gamma1 or alpha4Bbeta1gamma1 ) upon cotransfection with expression vectors for the beta1 and gamma1 subunits .