Specialized DNA polymerases (DNA pols) are required for lesion bypass in human cells. Auxiliary factors have an important, but so far poorly understood, role. Here we analyse the effects of human proliferating cell nuclear antigen (PCNA) and replication protein A (RP-A) on six different human DNA pols--belonging to the B, Y and X classes--during in vitro bypass of different lesions. The mutagenic lesion 8-oxo-guanine (8-oxo-G) has high miscoding potential. A major and specific effect was found for 8-oxo-G bypass with DNA pols lambda and eta. PCNA and RP-A allowed correct incorporation of dCTP opposite a 8-oxo-G template 1,200-fold more efficiently than the incorrect dATP by DNA pol lambda, and 68-fold by DNA pol eta, respectively. Experiments with DNA-pol-lambda-null cell extracts suggested an important role for DNA pol lambda. On the other hand, DNA pol iota, together with DNA pols alpha, delta and beta, showed a much lower correct bypass efficiency. Our findings show the existence of an accurate mechanism to reduce the deleterious consequences of oxidative damage and, in addition, point to an important role for PCNA and RP-A in determining a functional hierarchy among different DNA pols in lesion bypass.

The open chromatin of embryonic stem cells (ESCs) condenses into repressive heterochromatin as cells exit the pluripotent state. How the 3D genome organization is orchestrated and implicated in pluripotency and lineage specification is not understood. Here, we find that maturation of the long noncoding RNA (lncRNA) pRNA is required for establishment of heterochromatin at ribosomal RNA genes, the genetic component of nucleoli, and this process is inactivated in pluripotent ESCs. By using mature pRNA to tether heterochromatin at nucleoli of ESCs, we find that localized heterochromatin condensation of ribosomal RNA genes initiates establishment of highly condensed chromatin structures outside of the nucleolus. Moreover, we reveal that formation of such highly condensed, transcriptionally repressed heterochromatin promotes transcriptional activation of differentiation genes and loss of pluripotency. Our findings unravel the nucleolus as an active regulator of chromatin plasticity and pluripotency and challenge current views on heterochromatin regulation and function in ESCs.

The crystallization and subsequent polymorphic transformation from the β to the R form of glycine has been studied using optical microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy techniques. The crystal structure and morphology of β glycine have been determined, and the influence of solvent, solubility, and process scale on its solvent-mediated transformation to the R form was quantified. It is concluded that for the low solubility environments used in this study, the rate-determining step in the transformation process is the dissolution rate of the metastable β polymorph.

This contribution describes the kinetics of the solution mediated phase transformation between forms 1 and 2 of dihydroxybenzoic acid. It is shown how a combination of kinetic, morphological, and modeling data can be used to give a full description of the rate-determining process in such a transformation. Surprisingly, secondary nucleation is found to dominate the kinetic processes. Such a phenomenon is well-known in continuous crystallization but is reported here for the first time in a polymorphic phase transformation. This observation has significant consequences for process and product control in the pharmaceutical and specialty chemicals industries.

This paper explores the crystallization of glycine from aqueous solution within a variety of colloidal systems in which the dimension of the crystallization environment varies from micrometers to nanometers. The study focuses on the polymorphic outcome of crystallization experiments and the extent to which crystal size can be controlled. The appearance of the β and γ polymorphic forms is found to be related to the organization and functionality of the surfactants utilized as well as the supersaturation. Overall, it is noted that while macroemulsions may be used to generate particulates of controlled size, crystal growth in microemulsion and lamellar phases is not restricted to the dimensions of the aqueous domains.