A transposon insertion in ActA stops tail formation by L. monocytogenes. Does this fact alone prove that ActA is an actin nucleator? What were some other possibilities scientists had to consider...

A transposon insertion in ActA stops tail formation by L. monocytogenes. Does this fact alone prove that ActA is an actin nucleator? What were some other possibilities scientists had to consider before concluding that ActA is the only bacterial protein that participates in the actin polymerization process? How could you determine whether the actin polymerization factor was produced by the bacteria as opposed to being a host cell factor or protein?