Kinetics of nucleoside incorporation into nuclear and cytoplasmic rna

HeLa and conjunctiva tissue culture cells were incubated for various intervals with tritiated nucleosides and the incorporation into RNA was localized in different parts of the cell by means of autoradiography. In order to obtain quantitative measurements of incorporation from grain count data the influence of cell geometry on the absorption of the tritium/3 ray was considered. Relative correction factors, E = g/g*, relating an idealized grain count in the absence of absorption, g, to the actual grain count, g*, were derived for the different cell compartments. For the average HeLa cell the factors for the nucleolus, n, non-nucleolar parts of the nucleus, N, and the cytoplasm, C, are in the ratio En/EN/ Ee = 2.3/1.6/1.0. The kinetics of incorporation for cytidine and adenosine are similar. The n and N curves are characterized by a rapid rise and early saturation, whereas the C curves show an appreciable lag and no evidence of saturation for intervals as long as one generation time. Estimates of the relative amounts of RNA in each compartment were obtained from ultraviolet micro absorption measurements and used together with the kinetic data to calculate specific activities. For incubation periods of short duration the ratio of specific activities n/N for cytidine is approximately twice that for adenosine. Three hypotheses for the mechanism of ribonucleoside incorporation and RNA synthesis are discussed, and arguments favoring a transport of RNA or an RNA by-product from the nucleus and nucleolus to the cytoplasm are presented. © 1961, Rockefeller University Press. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Biphasic cellular adaptations and ecological implications of Alteromonas macleodii degrading a mixture of algal polysaccharides

Algal polysaccharides are an important bacterial nutrient source and central component of marine food webs. However, cellular and ecological aspects concerning the bacterial degradation of polysaccharide mixtures, as presumably abundant in natural habitats, are poorly understood. Here, we contextualize marine polysaccharide mixtures and their bacterial utilization in several ways using the model bacterium Alteromonas macleodii 83-1, which can degrade multiple algal polysaccharides and contributes to polysaccharide degradation in the oceans. Transcriptomic, proteomic and exometabolomic profiling revealed cellular adaptations of A. macleodii 83-1 when degrading a mix of laminarin, alginate and pectin. Strain 83-1 exhibited substrate prioritization driven by catabolite repression, with initial laminarin utilization followed by simultaneous alginate/pectin utilization. This biphasic phenotype coincided with pronounced shifts in gene expression, protein abundance and metabolite secretion, mainly involving CAZymes/polysaccharide utilization loci but also other functional traits. Distinct temporal changes in exometabolome composition, including the alginate/pectin-specific secretion of pyrroloquinoline quinone, suggest that substrate-dependent adaptations influence chemical interactions within the community. The ecological relevance of cellular adaptations was underlined by molecular evidence that common marine macroalgae, in particular Saccharina and Fucus, release mixtures of alginate and pectin-like rhamnogalacturonan. Moreover, CAZyme microdiversity and the genomic predisposition towards polysaccharide mixtures among Alteromonas spp. suggest polysaccharide-related traits as an ecophysiological factor, potentially relating to distinct ‘carbohydrate utilization types’ with different ecological strategies. Considering the substantial primary productivity of algae on global scales, these insights contribute to the understanding of bacteria–algae interactions and the remineralization of chemically diverse polysaccharide pools, a key step in marine carbon cycling