SUMMARYThe PIN family of proteins is best known for its involvement in polar auxin transport and tropic responses. PIN6 (At1g77110) is one of the remaining PIN family members in Arabidopsis thaliana to which a biological function has not yet been ascribed. Here we report that PIN6 is a nectary-enriched gene whose expression level is positively correlated with total nectar production in Arabidopsis, and whose function is required for the proper development of short stamens. PIN6 accumulates in internal membranes consistent with the ER, and multiple lines of evidence demonstrate that PIN6 is required for auxin-dependent responses in nectaries. Wild-type plants expressing auxin-responsive DR5:GFP or DR5:GUS reporters displayed intense signal in lateral nectaries, but pin6 lateral nectaries showed little or no signal for these reporters. Further, exogenous auxin treatment increased nectar production more than tenfold in wild-type plants, but nectar production was not increased in pin6 mutants when treated with auxin. Conversely, the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) reduced nectar production in wild-type plants by more than twofold, but had no significant effect on pin6 lines. Interestingly, a MYB57 transcription factor mutant, myb57-2, closely phenocopied the loss-of-function mutant pin6-2. However, PIN6 expression was not dependent on MYB57, and RNA-seq analyses of pin6-2 and myb57-2 mutant nectaries showed little overlap in terms of differentially expressed genes. Cumulatively, these results demonstrate that PIN6 is required for proper auxin response and nectary function in Arabidopsis. These results also identify auxin as an important factor in the regulation of nectar production, and implicate short stamens in the maturation of lateral nectaries.

Functional Escherichia coli 30S ribosomal subunits can be reconstituted in vitro. However, slow kinetics and sharp temperature dependence suggest additional assembly factors are present in vivo. Extract activation of in vitro assembly results in association of DnaK/hsp70 chaperone components with pre-30S particles. Purified DnaK, its cochaperones DnaJ and GrpE, and ATP can facilitate reconstitution of functional 30S subunits under otherwise nonpermissive conditions. A link has been observed between DnaK, 30S subunit components, and ribosome biogenesis in vivo as well as in vitro. These studies reveal a novel role for the DnaK/hsp70 chaperone system, in addition to its well-documented role in protein folding, and suggest that 30S subunit assembly can be facilitated.

We report results from a field experiment in which a randomized subset of newly hired workers at a large financial institution received a flyer containing information about the employer's 401(k) plan and the value of contributions compounding over a career. Younger workers who received the flyer were significantly more likely to begin contributing to the plan relative to their peers in the control group. Many workers do not participate in their employers' supplemental retirement savings programs, even though these programs offer substantial tax advantages and immediate returns due to matching contributions. From a survey of new hires we find that many workers choose not to contribute to the plan because they have other financial priorities. However, some non-participants lack the financial literacy to appreciate the benefit. These findings indicate that simple informational interventions can nudge workers to participate in retirement saving plans and enhance individual well-being and retirement income security.

We report results from a field experiment in which a randomized subset of newly hired workers at a large financial institution received a flyer containing information about the employer's 401(k) plan and the value of contributions compounding over a career. Younger workers who received the flyer were significantly more likely to begin contributing to the plan relative to their peers in the control group. Many workers do not participate in their employers' supplemental retirement savings programs, even though these programs offer substantial tax advantages and immediate returns due to matching contributions. From a survey of new hires we find that many workers choose not to contribute to the plan because they have other financial priorities. However, some non-participants lack the financial literacy to appreciate the benefit. These findings indicate that simple informational interventions can nudge workers to participate in retirement saving plans and enhance individual well-being and retirement income security.

Recently, there has been controversy regarding the ability of the DnaK chaperone system to facilitate Escherichia coli 30S subunit assembly at otherwise nonpermissive conditions. Here, we present additional data indicating that purified DnaK chaperone assembled 30S subunits are functional. Additionally, explanations for reported differences are discussed. Keywords: DnaK chaperone system; 16S rRNA; ribosome assemblyRibosome assembly is a highly complicated process that, despite years of work and the continuing efforts of many groups, is still not very well understood (for overview, see Williamson 2003). One avenue of research has been directed toward identifying extrinsic factors that facilitate assembly (for examples, see Alix and Guerin 1993;Charollais et al. 2003). Recently, Alix and Nierhaus (2003) reported experiments that appear to contradict our previous results showing that the DnaK chaperone system facilitates 30S subunit assembly under otherwise nonpermissive conditions (Maki et al. 2002). Here, we take the opportunity to reexamine the experiments performed by Alix and Nierhaus (2003) and to offer alternative explanations for the reported differences.To briefly summarize our findings (Maki et al. 2002), we first searched for cellular factors that facilitate 30S subunit assembly in vitro. Toward this end, we focused on a wellknown stall in assembly that occurs at low temperature and results in the production of an assembly intermediate, the 21S, reconstitution intermediate (RI) particle (Held and Nomura 1973;Traub and Nomura 1968). RI contains a subset of the small subunit ribosomal proteins and requires heat activation to assemble a full complement of proteins into a functional 30S particle. We observed that treatment of the intermediate with S100 extract at the nonpermissive temperature resulted in the formation of a peak that cosediments with 30S subunits, suggesting that factors that facilitate assembly were present in the extract. A nonribosomal protein was found associated with the intermediate, and N-terminal sequencing in combination with Western blot analysis identified this protein as DnaK. The purified DnaK chaperone system (DnaK, its two cochaperones, DnaJ and GrpE, and ATP) was shown to be sufficient to convert the sedimentation of the 21S RI particle to something resembling a 30S peak at the nonpermissive temperature. The appropriate ribosomal proteins were associated with this 30S peak after sucrose gradient sedimentation and purification. The purified particle was shown to have tRNA binding activity significantly above that of the assembly intermediate, although not as robust as the tRNA binding activity of 30S subunits formed by heat activation. Additionally, we demonstrated that DnaK selectively interacts with a subset of small subunit ribosomal proteins, of which S4 showed the strongest binding. Lastly, it was observed that overexpression of S4 could partially rescue phenotypic defects observed for a temperature-sensitive allele of dnaK (dnaK756). From these results, we conclud...