Figure 2. (A) Effect of carbon source on levels of crcZ and crcX. The values shown correspond to the ratios of the RNA levels observed for each condition relative to those observed in cells growing exponentially in LB medium as reference. The standard error is indicated. (B) Comparison of the abundance of crcZ relative to that of crcX under the specified growth conditions, determined by real-time RT-PCR. RNA samples were the same as those used in the assays presented in A.