cis and trans activation of globin gene transcription in transient assays.

Abstract

Effects of the SL 40 enhancer sequence on transcription of cloned human .alpha.- and .beta.-globin genes were examined shortly after their introduction into cultured mammalian cells. Detectable transcription of the .beta.-globin gene but not the .alpha.-globin gene requires linkage to the enhancer. The enhancer increases the amount of .beta.-globin RNA at least 100-fold but results in only a 5-10-fold increase in the amount of .alpha.-globin RNA. Plasmid replication does not increase the level of .beta.-globin RNA, regardless of linkage to the enhancer, but does result in an .simeq.50-fold increase in the level of .alpha.-globin RNA. The enhancer is not required for and does not increase transcription of either gene in 293 cells, an adenovirus 5-transformed human kidney cell line. An enhancer sequence is not required for activity of the normally enhancer-dependent SL40 early promoter in 293 cells, indicating that these cells contain a trans-acting factor(s) that circumvents the requirement for the enhancer sequence.