Protein L20 from the large subunit of Escherichia coli ribosomes is an assembly protein

When 50 S subunits from Escherichia coli are incubated in the presence of 4.3 m-LiCl, the resulting 4.3c core particle quantitatively lacks L20 in addition to other proteins. The 4.3c core can be reconstituted to an active 50 S subunit in the presence of total 50 S proteins by means of the second step incubation of the two-step reconstitution procedure. This finding indicates that the conformation of the 4.3c core is at least equivalent to the conformation of the reconstitution intermediate RI₅₀¹(1) particle, which is exclusively formed in the first-step incubation. It follows that L20 is not necessary for the maintenance of the 4.3c core conformation. In contrast, the total reconstitution of an active 50 S particle from (23 S + 5 S) RNA and a protein preparation lacking L20 was fully dependent on the addition of L20. However, when the 4.3c core, which does not contain L20, is reconstituted with the same protein fraction, the activity of the resulting particle did not depend on the presence of L20. Thus, L20 is essential for the early assembly (occurring in the first-step incubation) but plays no role either in the late assembly steps, or the functions of the mature 50 S particle.Heat treatment of the 4.3c core distorts the 4.3c core conformation and leads to particles with lower s values. The degradation of the 4.3c core conformation is reduced when L20 is added. A further stabilization is obtained by the addition of (L20 + L24). Thus, L20 is dispensable for the maintenance of the 4.3c core conformation, but stabilizes this conformation.     

Differentiation of Virus Types in Foot-and-Mouth Disease (FMD)

An improved complement-fixation technique in foot-and-mouth disease is described in details. In the development of the technique consideration has been given to the established presence of an antigen-excessphenomenon as well as to the linear relationship between amounts of immune serum used and complement fixed. The increased accuracy of the technique has made it possible more precise and rapid to detect even small serological differences.     

Evidence of taxon cycles in an Indo-Pacific passerine bird radiation (Aves: Pachycephala)

Many insular taxa possess extraordinary abilities to disperse but may differ in their abilities to diversify and compete. While some taxa are widespread across archipelagos, others have disjunct (relictual) populations. These types of taxa, exemplified in the literature by selections of unrelated taxa, have been interpreted as representing a continuum of expansions and contractions (i.e. taxon cycles). Here, we use molecular data of 35 out of 40 species of the avian genus Pachycephala (including 54 out of 66 taxa in Pachycephala pectoralis (sensu lato), to assess the spatio-temporal evolution of the group. We also include data on species distributions, morphology, habitat and elevational ranges to test a number of predictions associated with the taxon-cycle hypothesis. We demonstrate that relictual species persist on the largest and highest islands across the Indo-Pacific, whereas recent archipelago expansions resulted in colonization of all islands in a region. For co-occurring island taxa, the earliest colonists generally inhabit the interior and highest parts of an island, with little spatial overlap with later colonists. Collectively, our data support the idea that taxa continuously pass through phases of expansions and contractions (i.e. taxon cycles).     

SeqA limits DnaA activity in replication from oriC in Escherichia coli

A mutant Escherichia coli that transforms minichromosomes with high efficiency in the absence of Dam methylation has been Isolated and the mutation mapped to 16.25 min on the E. coli map. The mutant strain containing seqA2 is defective for growth in rich medium but not in minimal medium. A similar mutation In this gene, named seqA1, has also been isolated. Here we show that the product of the seqA gene, SeqA, normally acts as an inhibitor of chromosomal initiation. In the seqA2-containing mutant, the frequency of initiation increases by a factor of three. Introduction of the wild-type seqA gene on a low-copy plasmid suppresses the cold sensitivity of a dnaAcos mutant known to overinitiate at temperatures below 39°C. In addition, the seqA2 mutation is a suppressor of several dnaA (Ts) alleles. The seqA2 mutant overinitiates replication from oriC and displays the asynchronous initiation phenotype. Also the seqA2 mutant has an elevated level of DnaA protein (twofold). The introduction of minichromosomes or a low-copy-number plasmid carrying five DnaA-boxes from the oriC region increases the growth rate of the seqA2 mutant in rich medium to the wild-type level, reduces overinitiation but does not restore synchrony. We propose that the role of SeqA is to limit the activity level of the E. coli regulator of chromosome initiation, DnaA.     

New insights into the melanophilin (MLPH) gene controlling coat color phenotypes in American mink

The mutation causing the Silverblue color type (pp) is one of the most used recessive mutations within American mink (Neovison vison) fur farming, since it is involved in some of the popular color types such as Violet and Saphire which originate from a combination of recessive mutations. In the present study, the genomic and mRNA sequences of the melanophilin (MLPH) gene were studied in Violet, Silverblue and wild-type (wt) mink animals. Although breeding schemes and previous literature indicates that the Violet (aammpp) phenotype is a triple recessive color type involving the same locus as the Silverblue (pp) color type, our findings indicate different genotypes at the MLPH locus. Upon comparison at genomic level, we identified two deletions of the entire intron 7 and of the 5′ end of intron 8 in the sequence of the Silverblue MLPH gene. When investigating the mRNA, the Silverblue animals completely lack exon 8, which encodes 65 residues, of which 47 define the Myosin Va (MYO5A) binding domain. This may cause the incorrect anchoring of the MLPH protein to MYO5A in Silverblue animals, resulting in an improper pigmentation as seen in diluted phenotypes. Additionally, in the MLPH mRNA of wt, Violet and Silverblue phenotypes, part of intron 8 is retained resulting in a truncated MLPH protein, which is 359 residues long in wt and Violet and 284 residues long in Silverblue. Subsequently, our findings point out that the missing actin-binding domain, in neither of the 3 analyzed phenotypes affects the transport of melanosomes or the consequent final pigmentation. Moreover, the loss of the major part of the MYO5A domain in the Silverblue MLPH protein seems to be the responsible for the dilute phenotype. Based on our genomic DNA data, genetic tests for selecting Silverblue and Violet carrier animals can be performed in American mink.     

The morphological variation of some Crataegus populations (Rosaceae) in Greece and Yugoslavia

Morphological evidence of hybridization and introgression between Crataegus orien–talis Pallas ex M.–Bieb. and C. pycnoloba Boiss. & Heldr. in Boiss. was observed where the two species meet in the montane–subalpine zone of Mt Chelmos, Pelo–ponnisos. C. pycnoloba var. parnassica Diap. is a variant of C. orientalis. Greek and Yugoslavian material of C. monogyna Jacq., C. curvisepala Lindm. and their hybrid is compared with Danish material of the three taxa using the multivariate techniques of discriminant analysis and Wells' distance coefficient. The infraspecific variation of C. monogyna and the correct binary names for C. monogyna x orientalis ( C. x albanica Pojark. versus C. x polyacantha Jan) and C. curvisepala x monogyna (C. x kyrtostyla Fingerh.) are discussed.