Q. About Protein Expression !!!

[Miss ELLA CHAN]

  Hi,

  Could somebody kindly tell me what is the optimum OD600 for the induction
  of protein expression in bacterial strain using IPTG?  

  I have been heard that we can start the induction with OD600 = 0.6
  ie. the pre-log-phase or OD600 = 1.5 which is at the late log-phase.
  Which condition should be the best ??

  Thanks for your help !

   Regards,
   Ella