Nikkomycin Z counteracts Rylux BSU and Congo red inhibition of Saccharomyces cerevisiae growth but does not prevent formation of aberrant cell walls

Rylux BSU and Congo red bind to chitin, interfere with proper cell-wall ass embly, and stimulate chitin synthesis by increasing, most probably, chitin synthase 3 (ChS3) levels in Saccharomyces cerevisiae. On the other hand, th e antibiotic nikkomycin Z inhibits chitin synthesis competitively. As ChS3 is the critical target of nikkomycin Z, its effect was tested in cells inhi bited in growth by Rylux BSU or Congo red. Nikkomycin Z counteracted this i nhibition but did not counteract aberrant cell-wall formation. These result s indicate that chitin synthesis stimulation is the key step in Rylux BSU a nd Congo red inhibition and support the idea that increase in chitin synthe sis represents a compensatory response to damaged cell-wall structure. As R ylux BSU and Congo red bind to newly synthesized chitin, further damage is caused in the wall and the response works in this case contrariwise. Nikkom ycin Z breaks this vicious circle by counteracting the chitin synthesis sti mulation.