All isolates of L. monocytogenes secrete a protein of
60 kDa as a major extracellular product (27). The sequence
of the cloned gene predicts a basic protein of 484 amino acids
consisting of a 27-amino-acid signal sequence and an extended
repeat region consisting of 19 threonine-asparagine
units (26). Spontaneous rough mutants of L. monocytogenes
show reduced expression of p60 and form long chains which
possess double septa between the individual cells. Interestingly,
rough strains spontaneously revert to smooth isolates
and express normal amounts of p60. Rough mutants show a
decrease in invasiveness (27) but are relatively normal in
intracellular growth and polymerization of actin filaments