Candidate partitioning genes (parA and parB) for the linear chromosome of Streptomyces coelicolor were identified by DNA sequencing in a series of seven genes located between rnpA and trxA near the chromosomal replication origin. The most likely translation start point of parB overlapped the parA stop codon, suggestive of coregulation, and transcription analysis suggested that the two genes formed an operon. Deletion of part of parB had no effect on the growth or appearance of colonies but caused a deficiency in DNA partitioning during the multiple septation events involved in converting aerial hyphae into long chains of spores. At least 13% of spore compartments failed to inherit the normal DNA allocation. The same phenotype was obtained with a deletion removing a segment of DNA from both parA and parB. Reinforcing the idea of a special role for the par locus during sporulation, the stronger of two parAB promoters was greatly upregulated at about the time when sporulation septation was maximal in colonies. Three copies of a 14-bp inverted repeat (GTTTCACGT GAAAC) were found in or near the parAB genes, and at least 12 more identical copies were identified within 100 kb of oriC from the growing genome sequence database. Only one perfect copy of the 14-bp sequence was present in approximately 5 Mb of sequence available from the rest of the genome. The 14-bp sequence was similar to sequences identified as binding sites for Spo0J, a ParB homologue from Bacillus subtilis believed to be important for DNA partitioning

The origins of life likely required the cooperation among a set of molecular species interacting in a network. If so, then the earliest modes of evolutionary change would have been governed by the manners and mechanisms by which networks change their compositions over time. For molecular events, especially those in a pre-biological setting, these mechanisms have rarely been considered. We are only recently learning to apply the results of mathematical analyses of network dynamics to prebiotic events. Here, we attempt to forge connections between such analyses and the current state of knowledge in prebiotic chemistry. Of the many possible influences that could direct primordial network, six parameters emerge as the most influential when one considers the molecular characteristics of the best candidates for the emergence of biological information: polypeptides, RNA-like polymers, and lipids. These parameters are viable cores, connectivity kinetics, information control, scalability, resource availability, and compartmentalization. These parameters, both individually and jointly, guide the aggregate evolution of collectively autocatalytic sets. We are now in a position to translate these conclusions into a laboratory setting and test empirically the dynamics of prebiotic network evolution.

ABSTRACT:The purposes of this study were to (a) gain an understanding of the views of inquiry held by faculty members involved in undergraduate science teaching and (b) describe the challenges, constraints, and opportunities that they perceived in designing and teaching inquiry-based laboratories. Participants included 19 college professors, representing both life and physical science disciplines, from (a) 2-year community college, (b) small, private nonprofit liberal arts college, (c) public master's granting university, and (d) public doctoral/research extensive university. We collected data through semistructured interviews and applied an iterative data analysis process. College science faculty members held a "full and open inquiry" view, seeing classroom inquiry as time consuming, unstructured, and student directed. They believed that inquiry was more appropriate for upper level science majors than for introductory or nonscience majors. Although faculty members valued inquiry, they perceived limitations of time, class size, student motivation, and student ability. These limitations, coupled with their view of inquiry, constrained them from implementing inquiry-based laboratories. Our proposed inquiry continuum represents a broader view of inquiry that recognizes the interaction between two dimensions of inquiry: (a) the degree of inquiry and (b) the level of student directedness, and provides for a range of inquiry-based classroom activities.

Phylogenetic-comparative and mutational analyses were used to elucidate the structure of the catalytically active RNA component of eubacterial ribonuclease P (RNase P). In addition to the refinement and extension of known structural elements, the analyses revealed a long-range interaction that results in a second pseudoknot in the RNA. This feature strongly constrains the three-dimensional structure of RNase P RNA near the active site. Some RNase P RNAs lack this structure but contain a unique, possibly compensating, structural domain. This suggests that different RNA structures located at different positions in the sequence may have equivalent architectural functions in RNase P RNA.