We report the identification and initial characterization of paralemmin, a putative new morphoregulatory protein associated with the plasma membrane. Paralemmin is highly expressed in the brain but also less abundantly in many other tissues and cell types. cDNAs from chicken, human, and mouse predict acidic proteins of 42 kD that display a pattern of sequence cassettes with high inter-species conservation separated by poorly conserved linker sequences. Prenylation and palmitoylation of a COOH-terminal cluster of three cysteine residues confers hydrophobicity and membrane association to paralemmin. Paralemmin is also phosphorylated, and its mRNA is differentially spliced in a tissue-specific and developmentally regulated manner. Differential splicing, lipidation, and phosphorylation contribute to electrophoretic heterogeneity that results in an array of multiple bands on Western blots, most notably in brain. Paralemmin is associated with the cytoplasmic face of the plasma membranes of postsynaptic specializations, axonal and dendritic processes and perikarya, and also appears to be associated with an intracellular vesicle pool. It does not line the neuronal plasmalemma continuously but in clusters and patches. Its molecular and morphological properties are reminiscent of GAP-43, CAP-23, and MARCKS, proteins implicated in plasma membrane dynamics. Overexpression in several cell lines shows that paralemmin concentrates at sites of plasma membrane activity such as filopodia and microspikes, and induces cell expansion and process formation. The lipidation motif is essential for this morphogenic activity. We propose a function for paralemmin in the control of cell shape, e.g., through an involvement in membrane flow or in membrane–cytoskeleton interaction.

The mouse int-i gene is a putative mammary oncogene discovered as a target for transcriptionally activating proviral insertion mutations in mammary carcinomas induced by the mouse mammary tumor virus in C3H mice. We have isolated molecular clones of full-or nearly full-length cDNA transcribed from int-1 RNA (2.6 kilobases) in a virus-induced mammary tumor. Comparison of the nucleotide sequence of the cDNA clones with that of the int-1 gene (A. van Ooyen and R. Nusse, Cell 39:233-240, 1984) (MMTV) harbor proviral insertion mutations within a 30-kilobase (kb) region (21). The proviruses reside on either the 5' or 3' side of the int-1 transcriptional unit, usually oriented so that transcription of the provirus proceeds in the direction away from int-1 (22). These insertions are accompanied by the production of ca. 1 to 10 copies of int-1 mRNA per cell. Since the gene is silent in normal mammary tissue, it is likely that the proviral insertions are responsible for activating expression, presumably by an enhancer-like mechanism, and thereby contribute to mammary oncogenesis.Since int-1 has not been previously encountered as the progenitor of a retroviral oncogene and has not yet been shown to have neoplastic effects when introduced into cultured cells, the claim for its status as a cellular oncogene rests principally upon the frequency of transcriptionally activating MMTV insertion mutations of int-1 in mouse mammary tumors. To advance our understanding of the int-1 * Corresponding author.

WC report the cDNA-deduced primary structure of lhe chicken counterpart of the murine dilute gene product, a member of the myosin I family. Comparison of the chicken and mouse sequences reveals a distinct pattern ofdomains of high and low sequcncc conservation. An internal deletion of 25 amino acids probably reflects dil%renlial mRNA processing. Compared with other myosin heavy chain molecules, sequence similarity is highest with the M YO2 gene product of Succhuror?r,!xes cerevisiue. The M Y02 protein, implicated in vectorial vesicle transport, is homologous to the dihre protein over practically its entire length. In addition, the C-terminal domain of the dike protein is hi&ly similar to n putative giutamic acid dccarboxylasc sequence cloned from mouse brain. Ahcmativcly. this closely related clone might represent an isoTorm ol' the dllurc prowin derixvi from a second gene. potentially involved in genetic conditions related to dilute.

The mouse int-1 gene is a putative mammary oncogene discovered as a target for transcriptionally activating proviral insertion mutations in mammary carcinomas induced by the mouse mammary tumor virus in C3H mice. We have isolated molecular clones of full- or nearly full-length cDNA transcribed from int-1 RNA (2.6 kilobases) in a virus-induced mammary tumor. Comparison of the nucleotide sequence of the cDNA clones with that of the int-1 gene (A. van Ooyen and R. Nusse, Cell 39:233-240, 1984) shows the following. The coding region of the int-1 gene is composed of four exons. The splice donor and acceptor sites conform to consensus; however, at least two closely spaced polyadenylation sites are used, and the transcriptional initiation site remains ambiguous. The major open reading frame is preceded by an open frame 10 codons in length. The mRNA encodes a 41-kilodalton protein with several striking features--a strongly hydrophobic amino terminus, a cysteine-rich carboxy terminus, and four potential glycosylation sites. There are no differences in nucleotide sequence between the known exons of the normal and a provirally activated allele. The length of the deduced open reading frame was further confirmed by in vitro translation of RNA transcribed from the cDNA clones with SP6 RNA polymerase.

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