PMC

Schematic diagram illustrating that the PV replication complex is formed in cis. (A) ER membranes are altered by the expression of membrane-binding proteins, e.g., Cyt b₅ or PV protein 2C, or all of the PV nonstructural proteins encoded in the plasmid pE5PVΔP1. The altered membranes are not utilized (crossed arrows) in trans for PV replication complex formation during a subsequent PV infection. (B) Replication complex formation as it occurs during PV replication. Membrane-bound translation of viral RNA into protein (step 1) triggers the formation of vesicles on the ER (step 2). Vesicles carrying PV nonstructural proteins and previously translated RNA with initiated minus strand (step 3) form a viral replication complex (vesicular rosette) with replicating RNA in the replicative intermediate (RI) configuration (step 4). Hatched lines, RNA; stippled symbols, viral proteins.

PhtA couples nutrient acquisition to microbial differentiation at two stages of the L. pneumophila life cycle. PhtA threonine transport triggers intracellular transmissive L. pneumophila to differentiate to the replicative form (). Threonine acquisition by means of PhtA also is essential for L. pneumophila to replicate in macrophages (Figs. and ). When threonine acquisition by replicating bacteria is inefficient, L. pneumophila prematurely express transmission traits (), perhaps due to an early accumulation of the alarmone ppGpp.

Overview of difficult-to-replicate regions.
Simplified depiction of chromosomal regions that are ‘difficult-to-replicate’ and vulnerable to replicative stress. Proposed sources of replicative stress are also indicated. Common fragile sites (CFSs) often associate with long genes where stable association of the transcriptional machinery and RNA-DNA hybrids (R-loops) are found. Sparse replication origins within these genes also contribute to their vulnerability. Telomeres are composed of a GC-rich repetitive sequence, and G4 DNA structures and heterochromatic sub-telomeric regions exacerbate the challenge in replicating these regions. In the absence of a distal origin, fork convergence cannot overcome replication stalling. Centromeres and pericentromeric regions, spanning millions of base pairs in mammalian genomes, also comprise repetitive sequences. Non-B form DNA structures, R-loops and active transcription are found at centromeres, while pericentromeres are largely heterochromatic. The presence of origins within these regions remains unclear.

SlNAC1 Is Induced by TLCV Infection.
(A) TLCV infection results in an upregulation of SlNAC1 gene expression. RNA gel blot showing the expression of SlNAC1 in healthy (H) or TLCV-infected (I) tomato plants. Tissue samples were obtained at 0, 5, 10, 15, and 20 dpi.
(B) TYLCSV infection results in an upregulation of SlNAC1 gene expression. RNA gel blot showing the expression of SlNAC1 in healthy or TYLCSV-infected tomato plants. Tissue samples were obtained 0 and 25 dpi.
(C) Transient expression of REn is sufficient to induce SlNAC1 gene expression. Tomato leaves were infiltrated with A. tumefaciens cells containing a replication-competent TLCV 1.1mer, p35S, or p35S expressing the TLCV genes C1, C2, and REn. RNA was extracted from tissues 5 d postinfiltration and SlNAC1 expression analyzed by RNA gel blotting.
(D) A TLCV REn mutant cannot induce SlNAC1 gene expression. RNA gel blot showing the expression of SlNAC1 in healthy plants or plants infected with a TLCV REn mutant (REn-mut) at 0 and 25 dpi (top). The presence of replicating TLCV REn mutant was confirmed by DNA gel blotting (middle). In this blot, we also ran an extract obtained from plants infected with wild-type virus (left, designated M); the ratio of REn mutant:wild-type virus total nucleic acid extracts is 20:1. TLCV DNA species are marked RF (supercoiled double-stranded replicative form) and SS (single stranded).