Q1. Offer a model to explain how the F-box protein SLF and the S-RNase mediate self incompatibility. Be sure to account for the action of these proteins in compatible and incompatible interactions. Also state how the model explains competitive interaction.

Q2. Hydrophobic residues generally appear at the 1st and 4th positions in the seven-residue repeats of polypeptides that form coiled coils. (a) Why do polar or charged residues usually appear in the left over five positions? (b) Why is the sequence Ile-Gln-Glu-Val-Glu-Arg-Asp more likely than this sequence Trp-Gln-Glu-Tyr-Glu-Arg-Asp to show in a coiled form?