FIG. 2.

Characterization of the SPB1 gene. (A) Total RNA from a wild-type W303 strain was probed in a Northern blot experiment with a fragment of the SPB1 gene. The positions of the 25S and 18S rRNA are indicated on the right of the lane. A single band, one corresponding to an mRNA of 2.9 kb, was detected by this probe. (B) One of the two copies of the SPB1 gene was deleted in a diploid strain by insertion of a TRP1 marker (YBL4460). These cells were then sporulated and the four daughter spores were dissected by micromanipulation and grown on YPD plates. In each tetrad, only two spores were able to grow, all of which were Trp⁻, indicating that the gene is essential for spore development.