The intermediate spliceosomal C complex (also called the Bact or B(act) complex) is a very short-lived intermediate; the splicing intermediates are rapidly converted to splicing products. Also, the spliced products are released very rapidly, and no complex containing both the splicing products has been isolated. Conversion of the spliceosomal B complex to the spliceosomal C complex requires ATP. The extensive base-pairing between the U4 and U6 snRNAs is disrupted during the formation of the C complex, which is thought to require helicase-type activity associated with the DEAD box factors. The U4 snRNP and U1 snRNP dissociate from the complex and the LSM2-6 complex of the U6 snRNP is lost, apparently allowing the U6 snRNA to then base-pair with the U2 snRNA and the 5' end of the splice site on the mRNA (Bessonov et al. 2010).