Gene Expression Hot Paper Bidirectional Regulation of mRNA Translation in Mammalian Cells by Using PUF Domains**

Abstract: The regulation of gene expression is crucial in diverse areas of biological science, engineering, and medicine. A genetically encoded system based on the RNA binding domain of the Pumilio and FBF (PUF) proteins was developed for the bidirectional regulation (i.e., either upregulation or downregulation) of the translation of a target mRNA. PUF domains serve as designable scaffolds for the recognition of specific RNA elements and the specificity can be easily altered to target any 8-nucleotide RNA sequence. The expression of a reporter could be varied by over 17-fold when using PUFbased activators and repressors. The specificity of the method was established by using wild-type and mutant PUF domains. Furthermore, this method could be used to activate the translation of target mRNA downstream of PUF binding sites in a light-dependent manner. Such specific bidirectional control of mRNA translation could be particularly useful in the fields of synthetic biology, developmental biology, and metabolic engineering

Direct shoot organogenesis and plant regeneration from hypocotyl explants in selected genotypes of Leucaena leucocephala—A leguminous pulpwood tree

388-393An efficient in vitro plant regeneration system in subabul (Leucaena leucocephala), a leguminous pulp wood tree species, was established. The induction of shoots was achieved from selected elite clones of subabul K-8, K-636 and also wild type on MS medium supplemented with 2 % sucrose and different concentrations (0.88 to 24.6 μM) of plant growth regulators (BA, Kn, 2iP & TDZ). The best medium for shoot regeneration was MS with 22.2 μM BA (5 shoots per explant), followed by 22.7 μM TDZ (4.6 shoots per explant). Addition of putriscine (9.3 μM) to MS medium containing 22.2 μM BA enhanced the number of multiple shoots to 7-8 but not the frequency of response. Shoot initials (measuring 1 cm) when separated and transferred on to MS medium containing 1.4 μM GA₃ elongated to 2-5 cm in 15-20 d with 80% frequency. The per cent frequency of shoot differentiation was almost identical in the genotypes K-8 and K-636 but it differed significantly from the wild type. Leaf yellowing and abscission in all the genotypes was curtailed by supplementing the medium with 685 μM glutamine or 540 μM adenine. The excised shoots were transferred to root regeneration media containing 2.46 and 4.98 μM IBA or 2.6 and 5.3 μM NAA. Root regeneration was noticed with 100% frequency in all the three genotypes in presence of IBA or NAA. Plantlets were transferred successfully to the pots with 70% survival rate with no visible morphological variations. The protocol can be utilized for mass propagation and genetic transformation studies of this important pulpwood species