Messengers evolution 437

We have shown that the changes of signalling with senses have also been in a systematic sequence with oxidising conditions. The overall pattern of evolution of messengers was of a remarkable change in external carriers of information with a multiplication of varieties of a limited number of internal carriers ... 

E. coli maintains all of its genes in a state where they can be turned on or turned off on short notice. The short messenger lifetime makes it possible to control gene expression from the transcription level. The lack of separate compartments for RNA and protein synthesis has fostered mechanisms where translation actually exerts a direct role on transcription. These are some of the special features that have influenced the evolution of regulatory systems in E. coli. 

Beckman RJ, Schmidt RJ, Santerre PF PlutzkyJ, Crabtree GR, Long GL. The structure and evolution of a 461 amino acid human protein C precursor and its messenger Rna, based upon the DNA sequence of cloned human liver cDNAs. Acids Res 1985 13 5233-5247. 

Most receptors are proteins. Wishart (2005) noted that proteins are perhaps the most complex chemical entities in nature No other class of molecule exhibits the variety and irregularity in shape, size, texture, and mobility than can be found in proteins (proteins are discussed in more detail in Chapter 14). The tremendous diversity in proteins, and their specificity of shape and electrical charge, may be the reason for the evolution of their role as receptors. The best-characterized receptors are regulatory proteins. Regulatory proteins mediate the actions of endogenous messengers such as neurotransmitters and hormones, and this class of receptors mediates the effects of many of the most useful therapeutic agents (Bourne and von Zastrow, 2004). 

---