Purification of immunoglobulin heavy chain messenger RNA by immunoprecipitation from the mouse myeloma tumor, MOPC-31C

Immunoglobulin mu- and gamma-ribonucleic acid sequences in thymocytes and splenocytes from normal and hyperimmune mice

The immunoglobulin heavy-chain ribonucleic acid (RNA) repertoire of mouse thymocytes was examined. Previously, this laboratory reported immunoglobulin alpha-chain RNA sequences in mouse thymocytes [Near, R. I., & Storb, U. (1979 Biochemistry, 18, 964]. We have extended these studies to encompass mu, gamma 2b, and gamma 1 heavy-chain RNA sequences, mu-, gamma 2b-, and gamma 1-messenger RNAs (mRNAs) were purified from myelomas to 45, 22, and 54% purity, respectively. Each of these mRNAs faithfully translated into the appropriate immunoprecipitable protein in a reticulocyte lysate translation system. The gamma 1-mRNA translated into two major immunoprecipitable products of about 52 500 and 51 000 daltons while mu- and gamma 2b-mRNAs yielded only a single major protein. Complementary deoxyribonucleic acids (cDNAs) prepared from the mRNAs were used as hybridization probes and revealed the presence of about 70 mu-RNA sequences per average thymocyte as determined by hybridization kinetics, while gamma 1 and gamma 2b sequences were at the limits of detection. The mu-RNA sequences are present in the cytoplasm and are greater than 50% polyadenylated. Upon hyperimmunization of mice with sheep red blood cells, gamma 1-RNA in splenocytes increased by about 100-fold while only slightly increasing in thymocytes. mu and gamma 2b increased 2-3-fold in splenocytes and only slightly in thymocytes. The results argue against RNA sequences appearing in thymocytes due to contamination with peripheral confirmed with cloned cDNA probes. Thymocyte RNA analyzed by Northern blots displayed bands of the same size as those in splenocyte RNA or in purified mRNA when hybridized to mu, gamma 2b and alpha cloned probes. Also, K light-chain RNAs of the same size were found in spleen and thymus by using a cloned K-DNA probe. The results are consistent with the thymus containing mu-, alpha-, and K- and small amounts of gamma 1- or gamma 2b-RNAs coding for heavy- and light-chain-like proteins which may play a role in T-cell function.

A high production rate of translatable IgG mRNA accounts for the amplified synthesis of IgG in myeloma cells

The aim of the present work was to determine whether the accumulation of Ig mRNA in myeloma cells is due to a high rate of production or to a high stability of these molecules. Specific mRNAs for the light and heavy polypeptide chains of IgG were isolated from the murine MPC-11 myeloma tumor cells by immune precipitation of polysomes which synthesize these chains. It was found that the immune-precipitated polysomes were enriched 10--30-fold in the gamma and chi mRNA sequences respectively. In the wheat germ cell-free system the chi mRNA preparation was translated mainly into three polypeptides of Mr 25 000, 18 000, and 15 000. The method of immune precipitation of polysomes was also used to characterize three variant clones of MPC-11 myeloma. It was found that little if any gamma-chain polysomes are present in the L-chain producer and non-producer clones, while a substantial amount of chi-chain polysomes was present in the non-producer clone. This may be due to the presence in the non-producer cells of the constant region chi-chain fragment. In order to determine the relative synthesis rate of chi and gamma mRNAs, pulse-labelled polysomes were immune precipitated using antibodies to chi and gamma chains. It was found that chi and gamma mRNA molecules are produced at a very high relative rate each accounting for 10--15% of the total labeled mRNA after 1 h of labeling. These values are higher than the steady-state pool size of chi and gamma mRNA, which was 5--6%, and indicates that the half-life of these molecules is not unusually high. It is concluded that the amplified synthesis of immunoglobulin chains in myeloma cells is mainly due to a high rate of production of translatable chi and gamma mRNAs.

Purification of mouse immunoglobulin heavy-chain messenger RNAs from total myeloma tumor RNA

A procedure is described for the large-scale purification of light (L) and heavy (H) chain mRNAs from plasmacytomas produced in mice. Intact RNA is selectively precipitated in high yield from frozen tumors homogenized in 3 M LiCl and 6 M urea. L and H-chain mRNAs were purified by oligo(dT)-cellulose chromatography and either sucrose gradient centrifugation in conditions preventing aggregation or by means of high-resolution preparative gel electrophoresis under non-denaturing conditions. gamma 2a and alpha H-chain mRNAs sedimented as major components at 15.5 S and 16.5 S respectively, when L-chain mRNAs sedimented as 12-S species. H-chain mRNAs isolated by continuous elution during preparative gel electrophoresis were completely separated from both L-chain mRNA and residual 18-S rRNA, and migrated as single components of 1900 +/- 50 nucleotides on analytical denaturing gels. The partially purified H-chain mRNAs were translated into major components of molecular weights of 56,000 (gamma 2a) and 60,000 (alpha) in an mRNA-dependent rabbit reticulocyte lysate, whereas L-chain mRNAs yielded polypeptides of molecular weights of 25,000 (gamma) and 27,000 (chi). Up to 95% of the translation products directed by the purified mRNAs were immunoprecipitated using specific antisera. The purity of L and H-chain mRNAs was assessed by hybridization of corresponding cDNAs with excess recombinant plasmid DNA. The results indicated a minimum purity of 47% (gamma 2a), 62% (alpha), for H-chain mRNAs and 60% (chi), for L-chain mRNAs.

Immunoglobulin gamma 1 heavy chain gene: structural gene sequences cloned in a bacterial plasmid

Immunoglobulin gamma 1 heavy chain cDNA was cloned into an Escherichia coli plasmid pCR1 and its nucleotide sequence was determined. The hybrid plasmid contained approx. 900-bases-long gamma 1 chain cDNA sequence, including the complete sequence of the CH2 and CH3 domains and the 3' untranslated region, and partial sequence of the CH1 domain. The nucleotide sequence predicts an extra lysine at the carboxyl-terminus of the gamma 1 chain. Comparison of the nucleotide sequence of 3' untranslated regions of the immunoglobulin gamma 1 chain and kappa light chain showed a significant homology although lengths are quite divergent.

Mutual homology of mouse immunoglobulin gamma-chain gene sequences

We have assessed the relative homology of mouse immunoglobulin heavy-chain gene sequence using complementary DNAs (cDNAs) synthesized against gamma-chain mRNAs (gamma 1, gamma 2a, gamma 2b, and gamma 3) purified from mouse myelomas. cDNAs complementary to the gamma-chain mRNAs did not cross-hybridize with the mu- and alpha-chain mRNAs, whereas they cross-hybridized to significant extents (22--66%) with the gamma-chain mRNAs of other subclasses. The heterologous hybrids formed, however, melt at 5--13 degrees C lower temperatures as compared to the homologous hybrids, indicating that significant portions of the heterologous hybrids are mismatched. The rates of the cross-hybridization reactions are 2- to 17-fold slower than those of the homologous hybridization reactions. Therefore, the gamma-chain gene sequences of four subclasses share a part of homology with each other, but they are different enough to be measured separately. Cross-hybridization analysis indicate that the gamma 2a and gamma 2b genes are the most closely related, while the gamma 1 and gamma 3 genes are the least related among the gamma subclass genes.