The photosystem II reaction center protein D1 in Synechocystis sp strain 6803 is encoded by the psbA2 and psbA3 genes of the three-membered psbA gene family. The silent and divergent psbAl copy of the psbA gene family was activated by exchanging part of its upstream region with a corresponding fragment of the psbA2 copy. The light-regulated expression of the activated psbA7 gene showed that the inserted psbA2 segment contains the information necessary for light-dependent as well as high-light-stimulated transcription. The activated psbAl gene expressed a nove1 D1 protein, Dl'. A mutant strain containing psbA7 as the only active psbA gene grew photoautotrophically at a rate comparable to that of the wild type. This finding demonstrates that despite its unusual amino acid sequence, D1' is exchangeable for D1 in the photosystem II complex, at least under normal laboratory conditions. The D1' protein was found to have a degradation rate similar to that of the D1 protein under low-or high-light conditions. Another mutant containing the activated psbA1 gene together with the psbA2 and psbA3 genes produced both the D1 and D1' proteins.

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Summary Through differential screening of a cDNA library, we cloned six groups of genes that are expressed relatively early in the inoculated leaves of tobacco resisting infection by tobacco mosaic virus (TMV). Induction of all these genes was subsequently detected in the uninoculated leaves; thus, their expression is associated with the development of both local and systemic acquired resistance. Exogenously applied salicylic acid (SA) was observed to induce these genes transiently. However, analyses with transgenic NahG plants, which are unable to accumulate SA, demonstrated that expression of these genes in TMV‐inoculated leaves is mediated via an SA‐independent pathway. Because the expression kinetics of these genes differ from those associated with the well‐characterized pathogenesis‐related protein (PR‐1) and phenylalanine ammonia‐lyase (PAL) genes, we propose that they belong to a group which we designate SIS, for SA‐independent, systemically induced genes. Interestingly, the expression of several SIS genes in the uninoculated leaves of TMV‐infected NahG plants was delayed and/or reduced, raising the possibility that SA is involved in activating some of these genes in systemic tissue. Most of the SIS genes were induced by exogenous ethylene. However, analyses of infected NahG plants treated with ethylene action and/or synthesis inhibitors indicated that the TMV‐induced expression of several SIS genes is independent of ethylene as well as SA.

Background The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2) has had a major impact on world health over the last 2 years. The emergence of SARS-CoV-2 variants, particularly concerning variants, may affect the virus's pathogenicity, transmissibility, and vaccines potency. Both delta and the omicron variants have been designated by WHO as variants of concern. Methods and resultsIn this study, molecular techniques such as qPCR, conventional PCR, and sequencing were used to identify the first SARS-CoV-2 omicron variant that circulated in Iraq in January 2022. Bioinformatics and computational tools like phylogenetic analysis, predicted physical and chemical properties, stability, and molecular docking of the spike protein were used to compare the omicron with the delta variants. We found the receptor binding domain (RBD) and spike protein in omicron contain a greater number of hydrophobic amino acids compared to delta variant. We discovered a disorder-order conversion in RBD regions of the omicron variant, and this change may be important in terms of the effect of disordered residues/regions on spike protein stability and interaction with human angiotensin converting enzyme 2 (ACE2). Docking studies show that the omicron variant requires less energy to engage with ACE2, contributing to its higher binding affinity with human ACE2, consistent with more contagious transmission. Conclusion This is the first molecular study of the circulated omicron and delta variants in Iraq, showing that the omicron variant in Iraq had a higher affinity for ACE2 than the delta variant, which may lead to higher transmissibility.

Modified forms of the D1 protein with deletions in lumen-exposed regions, were constructed in the cyanobacterium Synechocystis 6803 using site-directed mutagenesis. Integration and stability of the mutated D1 proteins in the thylakoid membrane were studied by immunoblot and pulse-chase analyses. It was found that in Δ(N325-E333), the D1 protein with a deletion in the C-terminal tail, could insert in the thylakoids to normal amounts but its stability in the membrane was dramatically reduced. Insertion of D1 in Δ(V58-D61) or Δ(D103-G109);G110R, with deletions in the A-B loop, was severely obstructed, For Δ(P350-T354), with a deletion in the processed region of the C-terminus of D1, no phenotypic effects were observed. The effects of failed D1 insertion or accumulation on Photosystem II assembly was monitored by immunoblot analysis. The conclusions from these experiments are that the extrinsic 33 kDa protein, CP43, and the β subunit of cytochrome b559 accumulate in the thylakoid membrane independently of the D1 protein, and that accumulation of the D2 protein and CP47 requires insertion but not necessarily accumulation of the D1 protein.