Chen, Haiqi | Search NASA

DOE OSTI2022

In vivo hypermutation and continuous evolution

Directed evolution has revolutionized biomolecular engineering by applying cycles of mutation, amplification and selection to genes of interest (GOIs). However, classical directed evolution methods that rely on manually staged evolutionary cycles constrain the scale and depth of the evolutionary search that is possible. Here we describe genetic systems that achieve cycles of rapid mutation, amplification and selection fully inside living cells, enabling the continuous evolution of GOIs as cells grow. These systems advance the scale, evolutionary search depth, ease and overall power of directed evolution and access important new areas of protein evolution and engineering.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1989

Analysis of the velocity law in the wind of the Be star Lambda Pavonis

This paper reanalyzes the IUE spectra of Lambda Pavonis secured in 1982 (Sahade et al.). It is found that the profiles of the broad UV lines are either rotationally broadened or nonrotationally broadened and that the rotationally broadened profiles can be sorted out in two groups characterized by rotational velocity values of 170 km/s and of 210 km/s, respectively. From the analysis of the rotational and of the radial velocities it is possible to distinguish two regions in the extended atmosphere of the star, namely, a region which is rotating and a region which is expanding. In the rotating region, the radial velocities are about zero, and the rotational velocity increases from 170 km/s to 250 km/s. In the expanding region, the rotational energy dissipates, the wind is accelerated to a maximum of -155 km/s, and farther out it decelerates.

Chen, Haiqi↗