In two models for DNA replication and transcription, tra ditional one known as sliding model postulates that proteins involving replicati on and transcription track on the DNA template as a locomotive. In factory model proposed recently, those proteins are immobilized on nuclear structure, to pull the template. Growing evidence from biochemistry, biophysics, and cell biology suggests that the factory model is an actual fact in vivo.

The effect of pH on the extracellularpolysaccharide synthesis by Aureobasidium pullulans was studied by addding CaCO3and HCI. Cultivated in P2 liquid medium for 24h,pH dropped to 3. 6 because of strongly producing acid. Under this low pH environment, further fermentation for 120h,only 5. 9g/L of polysacharide was obtained. When grown in MP2 medium contaning0. 5 % CaCOs,the pH was kept above 5.0 during 144 hours,production of polysaccharide increased to 31g/L. The detailed information of effects of controlled pH on polysaccharide production showed an optimal pH value 5. 0 must be maintained through the fermentative period.

The effect of pH on the extracellularpolysaccharide synthesis by Aureobasidium pullulans was studied by addding CaCO 3and HCl.Cultivated in P2 liquid medium for 24h,pH dropped to 3.6 because of strongly producing acid.Under this low pH environment,further fermentation for 120h,only 5.9g/L of polysacharide was obtained.When grown in MP2 medium contaning0.5% CaCO 3,the pH was kept above 5.0 during 144 hours,production of polysaccharide increased to 31g/L. The detailed information of effects of controlled pH on polysaccharide production showed an optimal pH value 5.0 must be maintained through the fermentative period.