Regulation of Genes Encoding Plastid Proteins During Chloroplast Biogenesis in Euglena

Multiple and complex molecular mechanisms activate and coordinate the expression of genes that encode chloroplast proteins. These genes themselves are encoded both in the organelle’s own genome and in the nuclear genome. At least some of the nuclear genes are regulated at the transcrip-tional level.1 In other cases, and especially during chloroplast biogenesis, posttranscriptional regulation of nuclear genes appears to occur.2 For some chloroplast-encoded genes, a specific transcriptional control results from variations in the strengths of their promoter elements.3 Even so, the expression of these latter genes also appears to be strongly influenced by postranscriptional regulatory mechanisms occurring at the levels of mRNA stability and translation.3,4