Horizontal gene transfer (HGT) of DNA from the plastid to the nuclear and mitochondrial genomes of higher plants is a common phenomenon; however, plastid genomes (plastomes) are highly conserved and have generally been regarded as impervious to HGT. We sequenced the 158 kb plastome and the 690 kb mitochondrial genome of common milkweed (Asclepias syriaca [Apocynaceae]) and found evidence of intracellular HGT for a 2.4-kb segment of mitochondrial DNA to the rps2–rpoC2 intergenic spacer of the plastome. The transferred region contains an rpl2 pseudogene and is flanked by plastid sequence in the mitochondrial genome, including an rpoC2 pseudogene, which likely provided the mechanism for HGT back to the plastome through double-strand break repair involving homologous recombination. The plastome insertion is restricted to tribe Asclepiadeae of subfamily Asclepiadoideae, whereas the mitochondrial rpoC2 pseudogene is present throughout the subfamily, which confirms that the plastid to mitochondrial HGT event preceded the HGT to the plastome. Although the plastome insertion has been maintained in all lineages of Asclepiadoideae, it shows minimal evidence of transcription in A. syriaca and is likely nonfunctional. Furthermore, we found recent gene conversion of the mitochondrial rpoC2 pseudogene in Asclepias by the plastid gene, which reflects continued interaction of these genomes.

The skeletal abnormalities in growing alcohol-fed rats were due to a combination of effects specific to alcohol consumption and alcohol-induced caloric restriction.

SERPINB11, the last of 13 human clade B serpins to be described, gave rise to seven different isoforms. One cDNA contained a premature termination codon, two contained splice variants, and four contained full-length open reading frames punctuated by eight single nucleotide polymorphisms (SNPs). The SNPs encoded amino acid variants located within the serpin scaffold but not the reactive site loop (RSL). Although the mouse orthologue, Serpinb11, could inhibit trypsin-like peptidases, SERPINB11 showed no inhibitory activity. To determine whether the human RSL targeted a different class of peptidases or the serpin scaffold was unable to support inhibitory activity, we synthesized chimeric human and mouse proteins, in which the RSLs had been swapped. The human RSL served as a trypsin inhibitor when supported by mouse scaffold sequences. Conversely, the mouse RSL on the human scaffold showed no inhibitory activity. These findings suggested that variant residues in the SERPINB11 scaffold impaired serpin function. SDS-PAGE analysis supported this notion as RSL-cleaved SERPINB11 was unable to undergo the stressed-to-relaxed transition typical of inhibitory type serpins. Mutagenesis studies supported this hypothesis, since the reversion of amino acid sequences in helices D and I to those conserved in other clade B serpins partially restored the ability of SERPINB11 to form covalent complexes with trypsin. Taken together, these findings suggested that SER-PINB11 SNPs encoded amino acids in the scaffold that impaired RSL mobility, and HapMap data showed that the majority of genomes in different human populations harbored these noninhibitory SERPINB11 alleles. Like several other serpin superfamily members, SERPINB11 has lost inhibitory activity and may have evolved a noninhibitory function.Serpins are a superfamily of serine and cysteine peptidase inhibitors that contain ϳ1500 family members and are found in all domains of life (Eukarya, Eubacteria, and Archaea) as well as many Poxviridae (reviewed in Refs. 1-4). Unlike canonical inhibitors, inhibitory serpins employ a unique suicide substrate-like inhibitory mechanism to neutralize their target peptidases. The surface-exposed reactive site loop (RSL) 4 serves as a pseudosubstrate and binds to the active site of the peptidase. Upon cleavage of the RSL, the metastable serpin molecule undergoes a major conformational rearrangement and traps the covalently attached peptidase in a distorted, inactive form (5). A small proportion of serpins are noninhibitory and aid in diverse functions, such as hormone transport (e.g. SERPINA7/ thyroxine binding globulin) and protein folding (e.g. SER-PINH1/HSP47) (6, 7).Serpins are classified into 17 clades based on phylogenetic relationships (8). So far, 36 human serpins from nine clades (A-I) have been identified (2). The majority of serpins are plasma proteins that serve as critical regulators of important physiological processes, such as blood coagulation, fibrinolysis, and inflammation. In contrast, clade B serpins exist predominantly, but...