Fig. 2. mcph1 is the awol gene. (A) The Drosophila mcph1 gene structure. Exons are represented by filled boxes, 5'- and 3'-UTRs by open boxes, and splicing events by thin lines. The gene CG13189 lies within the largest intron of mcph1. Alternative splicing produces transcript mcph1-RA or -RB. Arrows below gene or transcript names indicate direction of transcription. Positions of the point mutations in each of the three EMS-induced alleles of awol and resulting amino acid changes (numbers refer to MCPH1-B) are indicated above the mcph1 gene. Imprecise excision of P-element EY11307 (inverted triangle) generated allele mcph1^Exc21 (deleted region indicated by gap). (B) Western analysis reveals trace amounts of or no MCPH1 protein in extracts of awol embryos relative to wild type (loading control: anti--tubulin). The excision allele (Exc21) of mcph1 serves as negative control. Df=Df(2R)BSC39, which removes the mcph1 genomic locus. (C) Comparison of the BRCT domain content (hatched boxes) of the two Drosophila MCPH1 isoforms (MCPH1-A and -B) and human MCPH1 protein (bottom). Positions of the amino acid changes in each of the three EMS-induced alleles of awol are indicated by asterisks. A double-sided arrow indicates the region of MCPH1-B used for antibody production.