We suggest the appearance of this band likely represents the extent to which GluN1 subunits have a weak propensity to form homodimers. Even though this observation is consistent with homodimerization of the GluN1 subunit, it does not mean that the GluN1 subunits form a homodimer in an intact NMDA receptor. Here we studied the association of ATDs within intact NMDA receptors and we found that ATDs form local heterodimers. The heteromeric NMDA receptor ATD is reminiscent of the GluA2 ATD in the GluA2 full-length structure. In the NMDA receptor, ATD heterodimers could also be arranged in a manner, although in this case the two ATD heterodimers will be arranged ��in parallel��, an arrangement that precludes an overall Histamine Phosphate two-fold axis of symmetry. Further experiments, such as the cross-linking of residues in the inter-heterodimer interface, are needed to clarify this issue. Small non-coding RNAs have emerged as potent regulators of gene expression at both the transcriptional and post-transcriptional levels. Recently, small RNAs that interact with Piwi proteins have been discovered in the mammalian germ line and in Drosophila. These Piwi-interacting RNAs represent a distinct small RNA pathway and differ from miRNAs in several ways. In flies, piRNA mutations lead to the overexpression and mobilisation of retrotransposons, which results in DNA lesions that cause germ line DNA damage. The biogenesis and mechanism of action of piRNAs is not well understood. For example, it is not known whether piRNAs primarily control chromatin organisation, gene transcription, RNA stability or RNA translation. Moreover, proteins involved in piRNA production have been implicated in the control of gene expression in somatic cells and in learning and memory. These data suggest that piRNAs might impact a broad range of biological processes. Studies in mice showed that piRNA-encoding regions are distributed over most chromosomes and range in size from 0.9 to 127 kb. Although piRNAs map exclusively to one chromosomal strand in many regions, some regions encode piRNAs in both orientations. In mammals, piRNAs predominantly map to a single genomic locus, whereas in flies they map to repetitive sites such as transposable elements. Betel et al. describes that 25% of piRNA clusters have 59 and 39 ends that coincide, indicating that they are not random degradation products of long transcripts. Because no stem and loop regions have been identified for piRNAs, it is possible that long-range dsRNA structure or sequence-specific protein machinery is involved in guiding the maturation process. In a recent study, we identified a genetic link between variants of intron 1 of the melatonin receptor 1A gene and calcium nephrolithiasis. In this study we conducted a bioinformatic analysis of this 22 kb genomic Shikonofuran-A region in order to identify possible regulatory elements. From this analysis, we identified the piR_015520-encoding region in intron 1 of the MTNR1A gene. Interestingly we demonstrate that the piRNA gene is expressed in human tissues and we show that this small RNA molecule is able to repress the expression of the melatonin receptor 1A gene. Specifically, reduced levels of the MT2 receptor-subtype and enhanced MT1 receptor expression have been described. Further, elevated expression of the MT1 receptor was found in malignant human breast epithelia compared to normal breast epithelia and stroma. To date, we do not know whether our data for piR_015520 represents a single case or a more general phenomenon. However, if this is also true for a different piRNA, then it is important to take it into account.