The human psi zeta globin gene, although nearly identical in sequence to the functional zeta globin gene, does not produce detectable levels of mRNA in human erythroid cells that do produce high levels of zeta mRNA. This observed inactivity of the psi zeta gene is unlikely to be caused by mRNA instability since hybrid alpha/psi zeta gene constructs produce high levels of mRNA in Cos7 cell transient expression assays. The analysis of zeta and psi zeta gene constructs stably integrated into a z...