The Streptomyces coelicolor dagA gene, coding for an extracellular aga
rase, has been propagated on a multicopy plasmid in S. coelicolor A3(2
), the natural agarase producer strain and in S. lividans TK21, a clos
ely related, nonproducer strain. The effect of the carbon source on th
e production of agarase by both strains, upon cultivation in liquid me
dium, revealed that the glucose repression affected the synthesis of a
garase at the level of secretion, rather than at the level of transcri
ption. In the presence of glucose, the pre-agarase was degraded intrac
ellularly and the overall secretion of proteases decreased considerabl
y in both strains, suggesting a negative regulatory role for glucose i
n the overall secretion in Streptomyces.