As the main service mode and management mode of socialized service, agricultural production trusteeship services (APTS) are an important way to realize the tight link between farmers and modern agricultural development, which is highly important for ensuring national food security. By constructing a utility model of farmers, this paper deduces the decision-making mechanism of farmers\' APTS from the dual mechanism of natural risk and non-agricultural employment income (NAEI) and uses the survey data of 956 farmers in the three northeastern provinces to verify the empirical results by using multivariate logit (Mlogit) and propensity score matching (PSM) methods. The research shows that natural risk hinders farmers\' choice of the APTS; NAEI has a positive impact on APST, and an increase in NAEI weakens the negative effect of natural risk on the choice of the APTS, and has an enhanced moderating effect. In addition, the scale heterogeneity analysis revealed that the impacts of natural risk and NAEI on farmers of different scales are significantly different. The NAEI adjustment effect has the greatest impact on small-scale farmers, followed by medium-scale farmers. In view of this, the government should stabilize the nonagricultural employment market and improve the nonagricultural employment opportunities of farmers. APTS organizations should transfer natural risks and improve the agricultural insurance system. According to the differences of different scales of farmers, different promotion policies are formulated, and the expansion of management and deepening services is proposed to further promote the development of APTS and consolidate the foundation of food security in China.

Protein-DNA interactions are an important class of biomolecular interactions inside the cell. Delineating the mechanisms of protein-DNA interactions and more specifically, how proteins search and bind to their specific cognate sequences has been the quest of many in the scientific community. Restriction enzymes have served as useful model systems to this end. In this work, we have investigated using molecular dynamics simulations the effect of L43K mutation on NaeI, a type IIE restriction enzyme. NaeI has two domains, the Topo and the Endo domains, each binding to identical strands of DNA sequences (GCCGGC)2. The binding of the DNA to the Topo domain is thought to enhance the binding and cleavage of DNA at the Endo domain. Interestingly, it has been found that the mutation of an amino acid that is distantly-located from the DNA cleavage site (L43K) converts the restriction endonuclease to a topoisomerase. Our investigations reveal that the L43K mutation not only induces local structural changes (as evidenced by changes in hydrogen bond propensities and differences in the percentage of secondary structure assignments of the residues in the ligase-like domain) but also alters the overall protein dynamics and DNA conformation which probably leads to the loss of specific cleavage of the recognition site. In a larger context, our study underscores the importance of considering the role of distantly-located amino acids in understanding protein-DNA interactions.