Regulation of plastid rDNA transcription by interaction of CDF2 with two different RNA polymerases

The plastid genome is known to be transcribed by a plastid-encoded prokaryotic-type RNA polymerase (PEP) and by a nucleus-encoded phage-type RNA polymerase (NEP). The spinach plastid rrn operon promoter region harbours three different, overlapping promoters. Two of them are of the prokaryotic type. The third promoter is a non-consensus-type NEP promoter. We separated three different transcriptional activities from spinach chloroplasts: PEP, the phage-type RNA polymerase NEP-1, and a third, hitherto undescribed transcriptional activity (NEP-2). NEP-2 specifically transcribes the rrn operon in the presence of the transcription factor CDF2. CDF2 was previously shown to recruit PEP to the rrn promoter to repress transcription. Together, our results suggest the existence of a third RNA polymerase in plastids and a mechanism of rDNA transcriptional regulation that is based on the interaction of the transcription factor CDF2 with two different transcriptional systems.

New core promoter element in RNA polymerase II-dependent transcription: sequence-specific DNA binding by transcription factor IIB

A sequence element located immediately upstream of the TATA element, and having the consensus sequence 5'-G/C-G/C-G/A-C-G-C-C-3', affects the ability of transcription factor IIB to enter transcription complexes and support transcription initiation. The sequence element is recognized directly by the transcription factor IIB. Recognition involves alpha-helices 4' and 5' of IIB, which comprise a helix-turn-helix DNA-binding motif. These observations establish that transcription initiation involves a fourth core promoter element, the IIB recognition element (BRE), in addition to the TATA element, the initiator element, and the downstream promoter element, and involves a second sequence-specific general transcription factor, IIB, in addition to transcription factor IID.

Trajectory of DNA in the RNA polymerase II transcription preinitiation complex

By using site-specific protein-DNA photocrosslinking, we define the positions of TATA-binding protein, transcription factor IIB, transcription factor IIF, and subunits of RNA polymerase II (RNAPII) relative to promoter DNA within the human transcription preinitiation complex. The results indicate that the interface between the largest and second-largest subunits of RNAPII forms an extended, approximately 240 A channel that interacts with promoter DNA both upstream and downstream of the transcription start. By using electron microscopy, we show that RNAPII compacts promoter DNA by the equivalent of approximately 50 bp. Together with the published structure of RNAPII, the results indicate that RNAPII wraps DNA around its surface and suggest a specific model for the trajectory of the wrapped DNA.

S2F, a leaf-specific trans-acting factor, binds to a novel cis-acting element and differentially activates the RPL21 gene

Tissue-specific factors control the differential expression of nuclear genes encoding plastid proteins. To identify some of these factors, the light-independent spinach RPL21 gene encoding the plastid ribosomal protein L21 was chosen as a model. The RPL21 promoter organization was defined by transient and stable transfections of RPL21 promoter deletion mutants fused to a reporter gene. The following results were obtained. (1) We identified a strong core promoter, spanning the transcription start site region, sufficient to drive high levels of gene expression. (2) We identified two non-overlapping positive and negative domains, located upstream from the core promoter region, that modulate core promoter activity independently of light. (3) We found that the positive domain contains a new cis-acting element, the S2 site, related to but different from the light-responsive GT-1 binding site. We show that the S2 site binds a leaf-specific nuclear factor (named S2F). The S2 site is conserved in the promoter region of many nuclear genes encoding plastid proteins. Experiments with transgenic tobacco plants confirmed that the S2 site is critical for positive domain activity in leaf tissues. The S2 site is thus identified as a new tissue-specific, light-independent regulatory element.

High-resolution mapping of nucleoprotein complexes by site-specific protein-DNA photocrosslinking: organization of the human TBP-TFIIA-TFIIB-DNA quaternary complex

We have used a novel site-specific protein-DNA photocrosslinking procedure to define the positions of polypeptide chains relative to promoter DNA in binary, ternary, and quaternary complexes containing human TATA-binding protein, human or yeast transcription factor IIA (TFIIA), human transcription factor IIB (TFIIB), and promoter DNA. The results indicate that TFIIA and TFIIB make more extensive interactions with promoter DNA than previously anticipated. TATA-binding protein, TFIIA, and TFIIB surround promoter DNA for two turns of DNA helix and thus may form a "cylindrical clamp" effectively topologically linked to promoter DNA. Our results have implications for the energetics, DNA-sequence-specificity, and pathway of assembly of eukaryotic transcription complexes.

The expression of nuclear genes encoding plastid ribosomal proteins precedes the expression of chloroplast genes during early phases of chloroplast development

The development of different plant organs (root, hypocotyl, and cotyledons) during seed germination is connected with the transformation of proplastids, which are found in embryonic and meristematic tissues, into amyloplasts in root tissues and into chloroplasts in cotyledons. We have analyzed the expression of nuclear and plastid genes coding for the plastid translational apparatus during the first 7 d of Spinacia oleracea development. Results show that the nuclear genes (rps1, rps22, rpI21, and rpI40) are expressed from the 1st d of seed imbibition and precede transcription of the chloroplast-encoded genes (photosynthetic and nonphotosynthetic), which starts the 3rd d after the beginning of imbibition. Transcription from the leaf-/cotyledon-specific P1 promoter of the rpI21 gene starts on the first imbibition day. Inhibition of chloroplast biogenesis by bleaching in the presence of norflurazon has no influence on the expression from this P1 promoter, suggesting that the onset of transcription of nuclear gene rpI21 is independent of a plastid signal.

Structure and expression of the nuclear gene coding for the chloroplast ribosomal protein L21: developmental regulation of a housekeeping gene by alternative promoters

We have cloned and sequenced the nuclear gene of the chloroplast ribosomal protein L21 (rpl21) of Spinacia oleracea. The gene consists of five exons and four introns. All introns are located in the sequence which corresponds to the Escherichia coli-like central core of the protein. L21 mRNA is present in photosynthetic (leaves) and nonphotosynthetic (roots and seeds) plant organs, although large quantitative differences exist. Primer extension and S1 nuclease mapping experiments revealed the existence of two types of transcripts in leaves. The two corresponding start sites were defined as P1 and P2. In roots and seeds, we found only the shorter of the two transcripts (initiated at P2). The nucleotide sequence surrounding P2 resembles promoters for housekeeping and vertebrate r-protein genes. Analysis of several promoter constructions by transient expression confirmed that both transcripts originate from transcription initiation. Results are interpreted to mean that the expression of the rpl21 gene is regulated by alternative promoters. One of the promoters (P2) is constitutive, and the other one (P1) is specifically induced in leaves, i.e., its activation should be related to the transformation of amyloplasts or proplastids to chloroplasts. The gene thus represents the first example of a housekeeping gene which is regulated by the organ-specific usage of alternative promoters. Primer extension analysis and S1 nuclease mapping of another nucleus-encoded chloroplast ribosomal protein gene (rps1) give evidence that the same type of regulation by two-promoter usage might be a more general phenomenon of plant chloroplast-related ribosomal protein genes. Preliminary results indicate that presence of conserved sequences within the rpl21 and rps1 promoter regions which compete for the same DNA binding activities.

Hypothesis for the evolutionary origin of the chloroplast ribosomal protein L21 of spinach

A full size cDNA clone encoding the chloroplast ribosomal protein L21 from spinach is presented. The identity of the clone and the location of the transit peptide processing site were determined by comparison with the N-terminal amino acid sequence of the spinach chloroplast protein CS-L7 previously identified. L21 r-protein sequences from spinach, Marchantia polymorpha and Escherichia coli are compared. Quite surprisingly, the data do not suggest that the rpl21 nuclear gene from spinach was derived through intracellular gene transfer from the chloroplast genome. The possibility of a mitochondrial origin for rpl21 gene of spinach is discussed.

[Proposal for a new descriptive psycho-physiopathological model of schizophrenia]

We present the conclusions of a study of pattern recognition in an intermittent luminous stimulation. This stimulation was stable on the one hand and on the other hand on fixed time basis (S.L.I. pulsations emitted by two flickers) and other associated tests (reaction time, Rorschach Test, etc). We have compared a population of 30 schizophrenics (French classification) and a reference group of 53 adult subjects of both sexes. We have not divided the patients into subclasses according to their symptoms. We have noticed in a significant manner the following signs: great vigilance at the beginning, decreasing very quickly, low attentiveness, a slowness of perception and motion, a weakness in the elaboration of decision processus, certain difficulties in defining the classification of objects, a modified perception of colours, a very feeble distinction of pertinent signals and of noise, an invasion by the internal stimulus, unbalanced compared to "outside", as in sensory deprivation, a great weakness in the processus of habituation and learning, a loss of the redundancy and the constancy of the outside world (or troubles of the internal coherency, as defined by Varela). The closure, the temporal troubles (historical and present) of the integration of signals are sufficient to explain these results. A model explains the deduced hypothesis on two levels: 1) historical: the troubles of habituation and learning prevent the formation of the inner stimulus (or image, representation); 2) present: closure, ambivalence (Gödel), troubles of associations, difficulties in detecting what is pertinent, hallucinations (a "delirious" internal stimulus). The specific brain-channels seem to be normal, on the contrary the non-specific channels and the channels of integration seem troubled. The temporal trouble of "present" seems to be located on a precocious precategorical iconic level. This descriptive model does not prejudge the etiology of the disease (bibliography).

[Comparison of the waking EEG with the subjective impressions of the waking individual (author's transl)]

Sleep EEGs of 30 chronic insomnia patients are compared with the patients' subjective estimation of the duration of sleep and the number of waking periods during the night's recording. Overall, the patients overestimated the duration of sleep and, to a lesser degree, the time they awaken in the morning. The number and duration of waking periods in the night were regularly underestimated, and no correlation could be found between the estimated number of waking periods and those actually recorded on the EEG. The composition of sleep on falling asleep and on waking, when these are overestimated, showed an appreciable period of waking sleep at these times (21% and 41% respectively). The authors suggest that their results indicate that study of the transitional periods of sleep and waking may provide a better understanding of insomnia and lead to alternative therapeutic approaches. They also indicate that the shorter duration of sleep is only one aspect of insomnia and other factors are probably important.