Autonomous assembly of synthetic oligonucleotides built from an expanded DNA alphabet. Total synthesis of a gene encoding kanamycin resistance.

Background: Many synthetic biologists seek to increase the degree of autonomy in the assembly of long DNA (L-DNA) constructs from short synthetic DNA fragments, which are today quite inexpensive because of automated solid-phase synthesis. However, the low information density of DNA built from just four nucleotide "letters", the presence of strong (G:C) and weak (A:T) nucleobase pairs, the non-canonical folded structures that compete with Watson-Crick pairing, and other features intrinsic to natural DNA, generally prevent the autonomous assembly of short single-stranded oligonucleotides greater than a dozen or so.

Results: We describe a new strategy to autonomously assemble L-DNA constructs from fragments of synthetic single-stranded DNA.

Kinetics and uptake mechanisms for monomethylmercury between freshwater algae and water.

Uptake kinetics of monomethylmercury chloride (MeHgCl) were measured for two species of green algae (Selenastrum capricomutum and Cosmarium botrytis), one blue-green algae (Schizothrix calcicola), and one diatom (Thalassiosira weissflogii), algal species that are commonly found in natural surface waters. Species differences were found with the two green algae giving the highest uptake rates, and one of them (Cosmarium) showing differences between cultures having widely different cell age (exponential versus stationary), where increases in uptake rate for cells 30 days old were about 25 times greater than cells only 3 days old when weights of cells were considered. Both Schizothrix and Thalassiosira exhibited nearly the same lower uptake rates, approximately 20 times lower than the two green algal species.