PLB1 and pituitary tumor: Again, hPL-A and hPL-B promoters are able to bind Pit-1 at equivalent sequences to those found in the hGH-N promoter [12,44], and ~0.5 kb hPL-A and hGH-N promoter sequences possess similar activity in transfected rat pituitary tumor cells in culture [45] (Figure 3A).