Article 5

Kaiser, C.A. & R. Schekman (1990) Distinct sets of SEC genes govern transport vesicle formation and fusion early in the secretory pathway. Cell 61: 723-733.

1. The authors of Article 5 uncovered a subtle phenotypic difference among the nine sec mutants described by Novick et al. (1981) (Article 4) as acting at the ER to Golgi step in secretion.

(a) Describe this phenotype.

(b) Which four sec mutants fall clearly into Class I and define this phenotype?

(c) Which three sec mutants fall clearly into Class II and define this phenotype?

(d) What do the authors mean when they say that the sec mutant phenotype was 'not allele specific'?

2. 'Double mutants were constructed by genetic crosses.' Give an example.

3. The data in Figure 3 indicate that Class I mutants are epistatic to Class II mutants. Discuss.

4. These results (Figure 3) are consistent with the hypothesis that Class I genes are involved in the formation of 50 nm vesicles and that Class II genes are involved in their consumption. Discuss.

The last part of Article 5 involves a genetic interaction study. We will return to this section of Article 5 later in the series after Article 10.

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