RNA Biol

Non-coding (nc)RNAs are important players in most biological processes. Although small RNAs such as microRNAs and small interfering RNAs have emerged as exceptionally important regulators of gene expression, great numbers of larger ncRNAs have also been identified. Many of these are abundant and differentially expressed but their functions have in most cases not been elucidated. The social amoeba Dictyostelium discoideum contain the ncRNAs commonly found in eukaryotes. In addition, we previously reported the identification of two novel classes of 42-65 nt long stem-loop forming RNAs, Class I and Class II RNAs, with unknown function. In this study we have further characterized these abundant ncRNAs, which are down regulated during development. We have confirmed expression of 29 Class I RNAs and experimentally verified the formation of the computationally predicted short conserved stem structure. Furthermore, we have for the first time created knockout strains for several small ncRNA genes in D. discoideum and found that deletion of one of the Class I RNAs, DdR-21, results in aberrant development. In addition we have shown that this Class I RNA forms a complex with one or several proteins but do not appear to be associated with ribosomes or polysomes. In a pull down assay, several proteins interacting with DdR-21 were identified, one of these has two RNA recognition motifs (RRMs). The purified RRM containing protein was demonstrated to bind directly and specifically to DdR-21

Revisiting the causal effects of exporting on productivity: Does price heterogeneity matter?

In most empirical studies that establish the export-productivity relationships, output is measured in values rather than in quantities. This makes it difficult to distinguish between productivity and within-firm changes in price that could occur following exposure to international markets. Using detailed data on quantity and prices from Ethiopian manufacturing firms in the period 1996-2005, this paper distinguishes efficiency from revenue based productivity and examines what this means for the estimated relationship between exporting and productivity. The main results show that exporters are more productive than non-exporters in terms of revenue based productivity and this is explained by both self-selection and learning effects. However, when correcting for price heterogeneity, exporters appear to be similar to non-exporters both before and after export entry. Overall, the results suggest that the increase in firm-level productivity following entry into foreign markets is associated with changes in prices as opposed to productive efficiency

Trade and human capital as determinants of growth

Do openness to trade and higher levels of human capital growth promote faster growth? To answer that question we use a panel of countries to investigate the role of human capital and two measures of openness in determining both the level of income and its growth rate. We argue that focusing on the levels of income by estimating a production function will give misleading estimates if there are unobserved differences in the underlying growth of technical efficiency across countries that are correlated with the explanatory variables. Using a growth rate equation, where we allow for country fixed effects and for possible endogeneity of explanatory variables, we show that both measures of openness, one the Sachs-Warner measure which reflects policy, and one from the PENN World Tables, the share of trade in GDP, give similar results. We argue that openness has a highly significant and large effect on the underlying rate of growth of productivity, while human capital does not. JEL classification: F43, O11

Are African manufacturing firms really inefficient? Evidence from firm-level panel data

Three dimensions of the performance of firms in Ghana’s manufacturing sector are investigated in this paper: their technology and the importance of technical and allocative efficiency. We show that the diversity of factor choices is not due to a non-homothetic technology. Observable skills are not quantitatively important as determinants of productivity. Technical inefficiency is not lower in firms with foreign ownership or older firms and its dispersion across firms is similar to that found in other economies. Large firms face far higher relative labour costs than small firms. If these factor market distortions could be removed substantial gains thorough improvements in allocative efficiency would be possible

Skills, Investment and Exports from Manufacturing Firms in Africa.

It has been argued that Africa will not be able to export manufactures as it lacks the necessary skills. This study uses panel data from Ghana to ask how skills have impacted on manufacturing investment and exports in the 1990s. Two dimensions of skills are defined and measured. The first is that observable in the education and experience of the workforce. The second is the underlying efficiency with which the firm operates. The latter is shown to be a significant determinant of both investment and exports. These exports are relatively capital intensive; unskilled labour-intensive exports remain negligible. Possible reasons for these outcomes are discussed

Sequence and generation of mature ribosomal RNA transcripts in Dictyostelium discoideum.

The amoeba Dictyostelium discoideum is a well-established model organism for studying numerous aspects of cellular and developmental functions. Its ribosomal RNA (rRNA) is encoded in an extrachromosomal palindrome that exists in ca. 100 copies in the cell. In this study, we have set out investigate the sequence of the expressed rRNA. For this, we have ligated the rRNA ends and performed RT-PCR on these circular RNAs. Sequencing revealed that the mature 26S, 17S, 5.8S and 5S rRNAs have sizes of 3741, 1871, 162 and 112 nucleotides, respectively. Unlike published, all mature rRNAs of a type uniformly display the same start and end nucleotides in the analyzed AX2 strain. We show the existence of a short-lived primary transcript covering the rRNA transcription unit of 17S, 5.8S and 26S rRNA. Northern blots and RT-PCR reveal that from this primary transcript two precursor molecules of the 17S and two precursors of the 26S rRNA are generated. We have also determined the sequences of these precursor molecules, and based on this data, we propose a model for the maturation of the rRNAs in Dictyostelium discoideum that we compare to the processing of the rRNA transcription unit of Saccharomyces cerevisiae