At the beginning of this reaction, 1 molecule of 'Elongin A1 protein', and 1 molecule of 'Elongin B:C complex' are present. At the end of this reaction, 1 molecule of 'Elongin Complex' is present. This reaction takes place in the 'nucleus' (Kibel et al. 1995, Aso et al. 1995, Duan et al. 1995).