Type IV collagen, a major structural component of basement membrane, has been characterized only in vertebrates. It is unique among the collagenous proteins in that it forms specific lattice networks by end-to-end interactions. In particular, in mammals the C-terminal noncollagenous domain (NCl) of collagen IV was shown to be one of the major cross-linking sites in the network assembly. Here, we give the first direct evidence of type-IV-related collagen in invertebrates by sequence analysis of cDNA and genomic DNA clones for the 3'-end of a previously characterized Drosophilu collagen gene. The data describe the C-terminal 190 amino acid residues of the triple helix and the entire noncollagenous domain (231 amino acids) of the chain encoded for by this gene. Comparison with data reported for human and mouse al(1V) chains reveals that triple-helix regions are quite different, while NC1 structures are very similar. This suggests different constraints on triple-helix and NC1 domains during evolution. Present data support the assumption that the NC1 structure originated from duplication of an ancestral sequence; the extent of both interspecies and intramolecular homologies suggests the maintenance in vertebrates and invertebrates of an ancestral specific function.Type IV collagen, the major macromolecular component of basement membranes, is now well characterized in mammals [l -61. It consists of triple-helical thread-like particles, probably composed of two different types of CI chains (al, a2) [l-2, 4, 71. These particles differ markedly from interstitial ones in that they comprise, in addition to the central triple helix, a noncollagenous globular domain (NC1) at the C-terminal end, and a short triple-helix domain (7s domain) at the N-terminal which enable them to form, by end-to-end interactions, a large lattice network instead of cross-striated fibrils [2, 3, 6, 81. Similar properties have been reported for an intestinal basement membrane collagen of the helminth Ascuris suum [9] and for a putative basement membrane collagen obtained from Drosophilu KCo cell cultures [5]. These observations, along with data on mammalian systems, have suggested that the ability to form end-to-end interactions is a general property of basement membrane collagens [S, 91. However, information on the fine structure of these binding sites is at present restricted to nucleotide and amino acid sequences of the NC1 domain of the a1 type-IV chains of human [lo] and mouse [ll] origin.Therefore, because of the widespread occurrence of basement membranes throughout animal phyla, as well as their implication in cell and tissue interactions of importance for morphogenetic events [12 -151, the characterization of type IV collagen genes in invertebrates is of particular interest from the point of view of both developmental biology and evolution.A evidence that DCgl encodes a type IV collagen chain by nucleotide sequencing of the 3'-terminal coding region of complementary and genomic DNA clones. The polypeptide predicted from the nucleotide seq...

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The methylation of cytoplasmic ribosomal RNA of cultured sycamore cells (Acer pseudoplatanus L.) was investigated. Labelled 17-S and 26-S rRNA were prepared from cells that had been incubated with either [32P]phosphate, methionine. Ion-exchange resin chromatography of 0.3 M KOH or 1 M HCl hydrolysates and two-dimensional chromatographic analyses of phosphodiesterase plus phosphatase digests of 17-S and 26-S rRNA were performed.17-S and 26-S rRNA contain 49 and 91 methyl groups per molecule, respectively. These values were verified in several ways. The high degree of methylation of sycamore rRNA, particularly for the 26-S rRNA, contrasts with the situation in all other investigated organisms.Several methylated bases were identified. 7-Methylguanine and 5-methylcytosine both occur in 17-S and 26-S rRNA. "-Methyladenine and N6,Nh-dimethyladenine are restricted to the 17-S rRNA while 3-methyluracil and 1 -methyladenine occur in the 26-S rRNA. One hypermodified uridine was also tentatively identified in the small rRNA. In 17-S rRNA, there is one copy of 7-methylguanine, N6-methyladenine and hypermodified uridine and two copies of N6,N6-dimethyladenine. 3-Methyluracil, 1-methyladenine and 5-methylcytosine occur twice, twice and three times, respectively, in 26-S rRNA. 7-Methylguanine and 5-methylcytosine are only in submolar amounts in the 26-S and 17-S rRNA, respectively.There are 40 & 2 and 83 f 3 2'-O-methylriboses per 17-S and 26-S rRNA molecule, respectively. In addition to the four 2'-O-methylnucleosides, one 2'-O-methylpseudouridine is present in the 17-S rRNA. Several lines of evidence argue for a non-random distribution of the methylriboses. In particular, one and seven Nm-Nm-Np structures occur in the 17-S and 26-S rRNA, respectively.The data are discussed comparatively with the methylation pattern of Escherichia coli, yeast and HeLa cell rRNA.The methylation of specific parts of polynucleotide chains is one of the multiple molecular events altering the primary transcriptional product of ribosomal genes and leading to the formation of the mature cytoplasmic rRNA [l]. Initial reports on the methylation of Escherichia coli rRNA and animal cytoplasmic rRNA suggested that eukaryotic cytoplasmic rRNA and prokaryotic rRNA strongly differ with regard to their type of methylation, the former being essentially ribose-methylated and the latter base-methylated. Later, specific methylated bases were identified in E. coli [2], yeast [3] and HeLa cells [4-61. These data supported the rather new idea that base-methylation might be an ancestral process widely conserved in living cells whereas ribose-methylation might represent a less-primitive process that appeared essentially in eukaryotic cells during evolution [l].With regard to cytoplasmic rRNA of higher plants, only 2'-O-methylation had been investigated [7-91. There had been no report on their basemethylation. Additional data on plant cells were

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