ASH IK AW A 



79 



the changes in the sedimentation pattern which indicate the appearance of new 

 microsomal particles [22, 23]. During the lag phase when less than 3 per cent 

 of the cells have visible buds, only the 80 S component (a peak in fig. 3) is pres- 

 ent in the ultracentrifuge pattern of cytoplasmic extract. As the cells begin to 

 proliferate and enter the log phase of growth (40 to 50 per cent visible buds), 

 four new microsomal components (3, y, 5, and £ peaks in fig. 3) appear in the 

 cell extracts. From log growth phase through stationary phase, the only change 

 in the sedimentation pattern appears to be in the ratio of these components. 

 Cell starvation is first evidenced by a decrease in the stability of the micro- 

 somes, which is indicated by the presence of polymerized material that sedi- 



(«) 



(*) 



to 



oo 



to 



(/) 



Fig. 3. Sedimentation photographs of microsomes isolated from 48-hour stationary-phase 

 cells 6 minutes after UTS at 200,0(%. (a) Yeast extract suspended in phosphate buffer 

 (0.00125 M KH 2 P0 4 -K 2 HP0 4 3:7, 0.001 M MgCU, and 0.01 M KCl) at 4° C for 1 day. (b) 

 Yeast extract suspended" in phosphate buffer at 4° C for 2 days, (c) After 7 days, (d) 

 After 10 days. (<?) After 13 days. (/) After 27 days. 



