FIG. 5.

Type II hCGβ reading frame usage. (A) Schematic of potential hCGβ1a, -2a, and -2b cDNA reading frames. Predicted translation products initiated at ATG₁ (black bars) or ATG₂ (gray bars) are depicted, and their sizes in amino acids (kDa) are indicated. Exons are depicted as open boxes, and the SanDI restriction site is shown by an arrowhead. (B) Autoradiography of protein products from hCGβ1a, -2a, or -2b cDNA labeled in rabbit reticulocyte (top) or wheat germ (bottom) cell-free transcription/translation systems. Short peptide bands are denoted by the white bracket. (C) Schematic of potential hCGβ1a, -2a, and -2b reading frames. Exons are depicted as open boxes. Reading frames are numbered 1 to 3 with subscript numbers denoting the order of ATG codons relative to the cDNA 5′ end. The first stop codon of each reading frame is numbered in gray. Linkage of the FFL gene to the 5′ part of hCGβ cDNAs is denoted by a dotted line for all F1 to F3 constructs and by a dashed line for the F1′ β2b construct. (D) Immunoblot of extract of HeLa cells transfected with reading frame constructs indicated. Blots were probed with antibodies (Ab) specific for firefly luciferase (FFL; top panel, short exposure; middle panel, longer exposure) and α-tubulin (Tub; bottom panel). (E) Relative luciferase activity in the same extracts as in panel D (n = 4 with duplicate samples).