Dependence of β1 tubulin expression on NF-E2.

(A) NF-E2–dependent expression of β1 tubulin in the megakaryocytic cell line L8057. Stable subclones that do not express p45 NF-E2 or express p45 NF-E2 alone or in combination with the small-Maf p18 subunit (designated as Neo, p45, or p45 + p18, respectively) have been generated. Expression of β1 tubulin protein is absent in the parental or mock-transfected lines and is restored in p45-expressing subclones and, to a greater extent, in subclones that overexpress both p45 and p18 proteins. Immunoblots using a monoclonal antibody reactive against all β tubulin isoforms (pan β) or rabbit anti-Tal1 serum are included as loading controls. Anti-p45 NF-E2 antibody reveals the absence of p45 protein in mock-transfected L8057 cells (Neo) (B) Semiquantitative RT-PCR analysis of β1 tubulin mRNA levels in embryonic (primitive) erythrocytes purified from p45 NF-E2^−/− and control (wild-type) yolk sacs. Equal loading of RNA is confirmed by PCR for the red blood cell–specific α-globin transcript, and the numbers of PCR cycles are indicated.