In this week's Science, a Harvard University-led team reports a new imaging technique for examining the layout of chromatin in individual chromosomes. The approach enables direct imaging and tracing of numerous genomic regions in individual chromosomes in situ, allowing for single-molecule analyses of chromatin organization that had not previously been possible. The researchers demonstrate their technique to reveal a number of new principles of chromatin organization.
Also in Science, researchers from Harvard and the Massachusetts Institute of Technology describe a method for building state machines — systems that exist in different states and where transitions between states are controlled by inputs — in living cells. To do so, the investigators took advantage of two chemically controlled recombinant enzymes capable of either inserting or excising DNA, which they used to encode states in DNA sequences. These states could then be read using either sequencing or PCR, as well as by regulation of gene expression. They demonstrated their approach by engineering state machines in Escherichia coli that used one, two, or three chemical inputs to control up to 16 DNA states. They also created a database to allow similar manipulation of more than 174,000 gene regulation programs, and expect their framework can be expanded to organisms other than bacteria with functional recombination enzymes.