“…Light/dark regulation of GUS transcript levels in Chlamydomonas chloroplast transformants carrying rbc L 59 end:GUS genes+ Transformants were grown in 12-h light/12-h dark cycles, total RNA was isolated at time points 11 h dark and 1 h light, and processed as described (legend to Fig+ 2; Materials and Methods)+ RNA gel blots were first hybridized to the atpB probe as a control and, after stripping of the membrane, to the GUS probe+ The increase upon illumination seen in abundance of transcripts of the endogenous atpB gene is due to increased transcription of the atpB gene in light and has been reported previously (Salvador et al+, 1993a)+ The membrane was exposed to X-ray film for 4 h for detection of atpB gene transcripts and for 24 h for detection of chimeric rbc L 59 end:GUS gene transcripts+ Numbers above the lanes denote nucleotide replacements in the rbc L 59 UTR sequence as depicted in Figures 1 and 2+ D: dark (also marked by a filled bar); L: light (also marked by an open bar)+ isolated by genomic complementation (Boudreau et al+, 2000)+ Putative cis-acting elements that are potential targets for RNA-stabilizing proteins have been localized in the 59 UTRs of chloroplast gene transcripts (Higgs et al+, 1999;Nickelsen et al+, 1999)+ A number of proteins were found in in vitro assays to bind to the 59 UTRs of Chlamydomonas chloroplast transcripts (Hauser et al+, 1996) and, in spinach, to the 59 UTRs of transcripts of genes that code for subunits of the ATP synthase complex (Hotchkiss & Hollingsworth, 1999)+ Although the identities and functions of these proteins have not been examined, it is possible that some of them are nucleus-encoded factors involved in mRNA stabilization+…”