The spinach CSP41 protein has been shown to bind and cleave chloroplast RNA in vitro. Arabidopsis thaliana, like other photosynthetic eukaryotes, encodes two copies of this protein. Several functions have been described for CSP41 proteins in Arabidopsis, including roles in chloroplast rRNA metabolism and transcription. CSP41a and CSP41b interact physically, but it is not clear whether they have...

Chloroplast genomes in land plants harbor approximately 20 group II introns. Genetic approaches have identified proteins involved in the splicing of many of these introns, but the proteins identified to date cannot account for the large size of intron ribonucleoprotein complexes and are not sufficient to reconstitute splicing in vitro. Here, we describe an additional protein that promotes chlor...

The chloroplast genome of land plants contains only a single gene for a splicing factor, Maturase K (MatK). To better understand the regulation of matK gene expression, we quantitatively investigated the expression of matK across tobacco (Nicotiana tabacum) development at the transcriptional, posttranscriptional, and protein levels. We observed striking discrepancies of MatK protein and matK me...

Evolution of the chloroplast from an endosymbiont to an organelle involved the transfer of many genes and regulatory functions to the nucleus, as well as a shift from mainly regulating the initiation of transcription to regulating additional, posttranscriptional steps (reviewed in Barkan, 2011). Sequence-specific RNA binding proteins, such as pentatricopeptide repeat (PPR) proteins, have signif...

Turnip yellow mosaic virus (TYMV), a positive-strand RNA virus in the alphavirus-like superfamily, encodes two replication proteins, 140K and 66K, both being required for its RNA genome replication. The 140K protein contains domains indicative of methyltransferase, proteinase, and NTPase/helicase, and the 66K protein encompasses the RNA-dependent RNA polymerase domain. During viral infection, t...

Viroids, small single-stranded circular RNAs (246-401 nucleotides), do not have mRNA capacity and must recruit host proteins to assist in the steps of their biological cycle. The nature of these cellular factors is poorly understood due to a lack of reliable experimental approaches. Here, to screen for host proteins interacting with viroid RNAs in vivo, we UV-irradiated avocado leaves infected ...

Under ionic conditions effecting little or no subunit dissociation, Chlamydomonas reinhardi contains 2 major classes of ribosomes with generic sedimentation velocities of 83 and 70s and 3 minor classes with sedimentation velocities of 66, 54, and 41 s. Ribosomal RNAs with sedimentation velocities of 25, 23, 18, 16 and 5 s have been identified. The 70-sribosomes are in the chloroplast and contai...

Prokaryotes possess a simple genome transcription system that is different from that of eukaryotes. In chloroplasts (plastids), it is believed that the prokaryotic gene transcription features govern genome transcription. However, the polycistronic operon transcription model cannot account for all the chloroplast genome (plastome) transcription products at whole-genome level, especially regardin...

The chloroplast genome of land plants contains only a single gene for a splicing factor, Maturase K (MatK). To better understand the regulation of matK gene expression, we quantitatively investigated the expression of matK across tobacco (Nicotiana tabacum) development at the transcriptional, posttranscriptional, and protein levels. We observed striking discrepancies of MatK protein and matK me...

Eukaryotic cells under stress repress translation and localize these messenger RNAs (mRNAs) to cytoplasmic RNA granules. We show that specific stress stimuli induce the assembly of RNA granules in an organelle with bacterial ancestry, the chloroplast of Chlamydomonas reinhardtii. These chloroplast stress granules (cpSGs) form during oxidative stress and disassemble during recovery from stress. ...