Activation of the genome of alfalfa mosaic virus is enhanced by the presence of the coat protein on all three genome parts.

The same amount of coat protein stimulates the infectivity of alfalfa mosaic virus RNA more when added to the three genome RNAs at once than when preincubated with one or two genome RNAs separately before the inoculum is completed. This suggests that the coat protein activates the genome by interacting with all three parts of it. It could not be demonstrated that infectivity is absolutely dependent on this multiple activation because of the possible exchange of protein between RNA molecules in the inoculum. However, factors that are likely to influence this exchange also have an effect on infectivity. Experiments showed that complex formation of coat protein with only the smallest genome RNA (that contains the coat protein gene) does not enhance infectivity as compared with other individual RNAs and protein combinations. Apparently the expression of the coat protein gene is not stimulated in this manner.